Unusual Peak Research Articles

Anomalous high-magnetic field electronic state of the nematic superconductors FeSe1−xSx

Understanding superconductivity requires detailed knowledge of the normal electronic state from which it emerges. A nematic electronic state that breaks the rotational symmetry of the lattice can potentially promote unique scattering relevant for superconductivity. Here, we investigate the normal transport of superconducting FeSe$_{1-x}$S$_x$ across a nematic phase transition using high magnetic fields up to 69 T to establish the temperature and field-dependencies. We find that the nematic state is an anomalous non-Fermi liquid, dominated by a linear resistivity at low temperatures that can transform into a Fermi liquid, depending on the composition $x$ and the impurity level. Near the nematic end point, we find an extended temperature regime with $T^{1.5}$ resistivity. The transverse magnetoresistance inside the nematic phase has as a $H^{1.55}$ dependence over a large magnetic field range and it displays an unusual peak at low temperatures inside the nematic phase. Our study reveals anomalous transport inside the nematic phase, driven by the subtle interplay between the changes in the electronic structure of a multi-band system and the unusual scattering processes affected by large magnetic fields and disorder

Anisotropic magnetoresistance and planar Hall effect in magnetoresistive NiFe/Pt thin film

The magnetoresistive NiFe/Pt sensor was fabricated by using standard microlithography and sputter deposition techniques and then the magnetic and magnetotransport properties were investigated. The magnetic properties of the sample show that the easy axis of magnetization prefers a predefined direction along the Hall bar. Moreover, the sample has uniaxial magnetic anisotropy due to the growth-induced magnetic anisotropy. On the other hand, the Anisotropic magnetoresistance (AMR) and the Planar Hall effect (PHE) of the sample were investigated in detail between 0° and 360°. The angle-dependent AMR and PHE signals at the in-plane magnetic field of constant magnitude intersect at certain angles. At these angles, the presence of unusual peaks and valleys was observed. This is proof that AMR and PHE curves had strongly affected each other at certain angles.

Penetrating Biological Tissue Using Light-Emitting Diodes with a Highly Efficient Near-Infrared ScBO3:Cr3+ Phosphor

Recently, infrared (IR) light-emitting diodes (LEDs) have attracted considerable interest in the research field worldwide. IR phosphors, the basic materials utilized in LEDs, have become a research hotspot as well. Here, we introduce the high-quantum-efficiency IR ScBO3:Cr3+ phosphor, which provides a spectral range of emission from 700 to 1000 nm with a peak maximum at 800 nm. Electron paramagnetic resonance spectroscopy, with high element selectivity, was used to elucidate the unusual small peak in the photoluminescence spectrum. Phonon structure and electron–lattice interaction were well observed and discussed via temperature-dependent measurements. Moreover, the high quantum efficiency of 72.8% was achieved. To evaluate their potential practical application, phosphor-converted LED packages were designed, which revealed high stability and high output power of 39.11 mW. Furthermore, the fabricated IR LED demonstrated a remarkable ability to penetrate biological tissues. This study provides insights into the luminescent properties and the practical applications of IR LEDs.

Single crystal growth, structural and transport properties of bad metal RhSb2**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674375, 11634015, 11925408, and 11674369), the National Basic Research Program of China (Grant Nos. 2016YFA0300600, 2016YFA030240, 2017YFA0302901, and 2018YFA0305700), the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant

We have successfully grown an arsenopyrite marcasite type RhSb2 single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb2 shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with ne = 8.62 × 1018 cm−3 at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with ab-initio band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb2. In addition, a large thermopower S(T) about –140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.

Spectroscopic features of natural and HPHT-treated yellow diamonds

High pressure high temperature (HPHT) treatment has long been applied in the gem trade for changing the body colour of diamonds. The identification of HPHT-treated diamonds is a field of on-going research in gemological laboratories, as different parameters of treatment will result in either the creation or the destruction of a variety of lattice defects in diamonds. Some features that exist in treated diamonds can also be found in natural diamonds, and consequently must not be employed for the separation of treated and natural diamonds. In this research, we investigated the properties of 11 natural yellow diamonds (directly obtained from the Ekati Diamond Mine to ensure that they are untreated) before and after HPHT treatment, conducted at a temperature of 2100 °C and a pressure of 6 GPa for 10 min. We report spectroscopic data and fluorescence characteristics, collected using PL mapping, FTIR mapping and fluorescence imaging showing the distribution of lattice defects and internal growth structures. PL mapping indicates SiV defects exist in one of the nitrogen-rich natural diamonds prior to treatment. Silicon-related defects can also be created by HPHT treatment, and they seem to show a relationship with pre-existing NV− centres. SIMS analysis was conducted to confirm the presence of silicon in these diamonds. The increase in the hydrogen-related infrared absorption peak at 3107 cm−1 (VN3H) is very strong in some diamonds that do not form B-centres during treatment. NVH was observed in our HPHT-treated natural diamonds, so it is possible that this strong increase in VN3H suppresses the aggregation of A- to B-centres as the newly formed A-centres were captured by NVH lattice defects to form VN3H. HPHT-altered and HPHT-induced platelet peaks are different from their natural counterparts in peak width and shape. Strong green fluorescence over a large area of a diamond, which is linked to relatively high concentration of H3 centres, was produced after HPHT treatment. We are confident that the unusual platelet peaks and strong emission of H3 centres are reliable indicators for HPHT-treated diamonds as they are not observed in untreated natural diamonds.

Morphology-sensitive infrared absorption bands of polymers derived from surface polaritons

Infrared (IR) spectroscopy is mostly used for analysis of normal modes, which provides rich chemical information of molecular structure at each chemical group. In practice, however, we sometimes encounter an unusually broad peak that cannot be assigned to a normal mode or overlapped multiple normal modes. This unusual peak can readily be understood by taking the concept of polariton into account even for a polymeric material. In general, however, ‘polariton’ is used for discussing inorganic crystals, in which the real part of the relative permittivity falls in negative. Here, we show some polymeric materials exhibit apparent negative relative permittivity in an IR region, which yields the unusual peaks. Through the measurements and theoretical simulations of spectra of polymer thin films, polariton is found to be necessary to comprehensively understand IR spectra of a polymer not only for a thin film, but also for powder dispersed in a KBr pellet, since the polariton peaks are found to be deeply correlated with the surface morphology.

Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)4As4 single crystals

We study the correlation between chemical composition and vortex dynamics in Ni-doped $\mathrm{CaK}{(\mathrm{F}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{i}}_{x})}_{4}\mathrm{A}{\mathrm{s}}_{4}$ ($x=0$, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities ${J}_{c}$ and the flux creep rates $S$. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent \ensuremath{\mu} within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (${U}_{0}l100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). The undoped crystals display modest ${J}_{c}$ values at low temperatures and high magnetic fields applied along the $c$ axis. ${J}_{c}(T)$ dependences at high fields display an unusual peak. The enhancement in ${J}_{c}(T)$ matches with an increase in ${U}_{0}$ and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in ${T}_{c}$ there is a nonmonotonic change in ${J}_{c}$. Initially ${J}_{c}$ increases, reaching a maximum value for $x=0.015$, and then ${J}_{c}$ decreases for $x\ensuremath{\ge}0.025$. This change in ${J}_{c}$($x$) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of ${J}_{c}(H)$ also manifests a change in behavior between these $x$ values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent \ensuremath{\mu} with Ni content, $x$. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation.

Surface barriers and field direction dependent vortex phase diagrams of YBa2Cu3−xAlxOδ for H c

We report the observation of an unusual field direction dependent second magnetisation peak (SMP) anomaly at very low fields, close to the field of full penetration Hp, in an aluminium-doped single crystal of YBa2Cu3−xAlxOδ, for H c. Such an anomaly is observed at different field values in the field ramp-up direction (H) compared to the field-down direction (H), and it is also found to persist to different temperatures. For the field-up direction, it is observed in the range of 8 K to 30 K (upper range extendible to 40 K depending on the crystal), while for the field-down direction, it is observed between 8 K to 65 K (upper range extendible to 70 K depending on the crystal). The temperature dependence of the fields of full penetration Hp, the onset field of the SMP anomaly, as well as the central magnetisation peak, seem to be affected by surface barriers at low temperatures, where they are seen to rise anomalously. An exponential fit to the low temperature penetration field and central magnetisation peak width, as well as an asymmetric magnetisation towards the irreversibility field, illustrate the effect of surface barriers at low temperatures. At higher temperatures, the onset field of the SMP anomaly is described well by a dislocation mediated order–disorder transition. The temperature dependence of the peak field of the second magnetisation anomaly, however, does not seem to be affected by the surface barrier and is well described by a power law. An oxygen deficient aluminium cluster model is used to explain the differences in the SMP anomalies in the two quadrants. Two vortex phase diagrams, one for each field direction, have been made describing the various phases.

Structural transformation and chemical modifications of the unusual layered zeolite MWW form SSZ-70

SSZ-70 is one of several layered forms of zeolite MMW obtained by direct synthesis with consecutive layers shifted by approximately ±1/3 of a unit cell in the horizontal direction (⟨110⟩), according to the recent structure solution report. Zeolite MWW is a valuable industrial alkylation catalyst and SSZ-70 itself was called by the inventors 'a successful catalytic material'. SSZ-70 shows characteristic powder X-ray diffraction pattern (XRD), containing a unique broad band with a roughly triangular shape and maximum at 8.5–9.0° 2θ (Cu Kα radiation), which can be used to distinguish SSZ-70 from the other MWW materials with different layer arrangements. This work concerns post-synthesis treatments of SSZ-70 to investigate its ability to produce more expanded structures by silylation, swelling and pillaring. Both boron- and aluminum-containing SSZ-70 were investigated. They showed the ability for interlayer expansion by swelling with cationic surfactants and were pillared with silica to produce micro/mesoporous hybrids with increased BET area. Not too surprisingly, the original unique layer stacking of SSZ-70 seems to have become more random and not distinguishable from the swollen forms of the other swellable MWW materials MCM-22 P and the monolayer MCM-56. Calcined SSZ-70 zeolites showed an unusual peak, assigned to (002) reflection, with d-spacing shorter than c-unit cell of the 3D MWW framework, which suggests collapse with formation of the so-called sub-zeolite form. Silylation resulted in different outcomes for B and Al SSZ-70 samples. The former produced interlayer expanded (IEZ) forms of B-SSZ-70 but did not show significant increase in pore volume and BET surface area. Silylation of Al-SSZ-70 did not yield the stabilized (IEZ) form but had a positive effect as it prevented the collapse to sub-zeolite upon calcination. Catalytic testing was carried out for the Al-containing SSZ-70 obtained by direct synthesis and for B-SSZ-70 activated by Al insertion. The former showed much higher concentration of Brønsted acid sites and 5 times faster conversion in a model alkylation reaction between benzyl alcohol and mesitylene. Pillared Al-SSZ-70 showed highest activity despite lower Al concentration due to silica pillars. Both silylation and pillaring had a positive effect on the activity in alkylation reaction with bulky molecules.

Potential detection of illegal fishing by passive acoustic telemetry

Acoustic tagging is typically used to gather data on the spatial ecology of diverse marine taxa, informing questions about spatio-temporal attributes such as residency and home range, but detection data may also reveal unanticipated insights. Many species demonstrate predictable site fidelity, and so a sudden cessation of detections for multiple individuals may be evidence of an atypical event. During 2013 and 2014, we acoustically tagged 47 grey reef sharks (Carcharhinus amblyrhynchos) and 48 silvertip sharks (Carcharhinus albimarginatus) near reefs in the British Indian Ocean Territory (BIOT) Marine Protected Area (MPA). From March 2013 to November 2014 inclusive, tags were ‘lost’, i.e. permanently ceased to be detected within the monitoring area, at an average rate of 2.6 ± 1.0 tags per month. Between 1 and 10 December 2014, detection data suggest the near-simultaneous loss of 15 of the remaining 43 active tagged sharks, a monthly loss rate over five times higher than during the previous 21 months. Between 4 and 14 December of 2014, the BIOT patrol vessel encountered 17 vessels engaged in suspected illegal fishing in the northern BIOT MPA; such sightings averaged one per month during the previous 8 months. Two of these vessels were arrested with a total of 359 sharks on board, of which grey reef and silvertip sharks constituted 47% by number. The unusual and coincident peaks in tag loss and vessel sightings, and the catch composition of the arrested vessels, suggest illegal fishing as a plausible explanation for the unusual pattern in our detection data. A Cox proportional hazards model found that the presence of fishing vessels increased the risk of tag loss by a factor of 6.0 (95% CI 2.6–14.0, p < 0.001). Based on the number of vessels sighted and the average number of sharks on vessels arrested in BIOT during 2014, we conservatively estimate that over 2000 sharks may have been removed during the suspected fishing event. Based on average catch compositions, over 1000 would have been grey reef and silvertip sharks. Assuming a closed population mark-recapture model, over one-third of the locally resident reef sharks may have been removed from the monitoring area. The data suggest that even sporadic fishing events may have a marked impact on local reef shark populations, but also demonstrate the potential of electronic tagging a tool for detecting illegal or otherwise unreported fishing activity.

The origin of the unusual DSC peaks of supercooled barium disilicate liquid

Crystallization proceeds through high-temperature and non-stoichiometric phases which recrystallize to become sanbornite (BaSi2O5) during heating or through time.

Using dissolved organic matter fluorescence to identify the provenance of nutrients in a lowland catchment; the River Thames, England

Catchment based solutions are being sought to mitigate water quality pressures and achieve multiple benefits but their success depends on a sound understanding of catchment functioning. Novel approaches to monitoring and data analysis are urgently needed. In this paper we explore the potential of river water fluorescence at the catchment scale in understanding nutrient concentrations, sources and pathways. Data were collected from across the River Thames basin from January 2012 to March 2015.Analysing emission excitation matrices (EEMs) using both PARAFAC and optimal area averaging produced consistent results for humic-like component 1 and tryptophan-like component 4 in the absence of a subset of samples that exhibited an unusual peak; illustrating the importance of inspecting the entire EEM before using peak averaging methods. Strong relationships between fluorescence components and dissolved organic carbon (DOC), soluble reactive phosphorus (SRP), and ammonium clearly demonstrated its potential, in this study basin, as a field based surrogate for nutrients. Analysing relationships between fluorescence, catchment characteristics and boron from across the basin enabled new insights into the provenance of nutrients. These include evidence for diffuse sources of DOC from near surface hydrological pathways (i.e. soil horizons); point source inputs of nutrients from sewage effluent discharges; and diffuse contributions of nutrients from agriculture and/or sewage (e.g. septic tanks).The information gained by broad scale catchment wide monitoring of fluorescence could support catchment managers in (a) prioritising subcatchments for nutrient mitigation; (b) providing information on relative nutrient source contributions; and (c) providing evidence of the effectiveness of investment in pollution mitigation measures. The collection of high resolution fluorescence data at the catchment scale and, in particular, over shorter event timescales would complement broad scale assessments by enhancing our hydro-biogeochemical process understanding.

Application of holographic interferometry for study rotor stator interaction in turbomachines

In article take up two examples application of holographic interferometry for investigation modes vibrations spinning bladed discs of engines and analysis vibrations taking into account rotor stator interaction.In the first example blade vibration measurement on operating compressor were carried out to investigate the extent of blade excitation of impeller. Interesting responses of the radial blades to the excitation were obtained with the compressor with the cambered vane diffuser. Unusual and unexpected significant resonance peaks of blade were observable when rotating frequency is near 18000 rpm with maximum stress amplitudes. A vibration test at rest using holographic interferometry was carried out by taking an interferogram of the impeller with one diameter and circle.In present paper for the first example was shown that strong impeller vibration excited by the diffuser vanes is due to interaction between impeller and diffuser vanes and spinning impeller oscillated with mode one diameter and circle.In the second example vibrations wheel of turbine was investigated on holographic test stand and during spinning test. At work turbine wheel consisting of stage was find out that dangerous stresses with frequency about 8000 Hz arise from the action of 28 harmonic. At investigation of this wheel on the holographic stand was find mode with 7 diameters on the frequency 7893 Hz.Strong turbine vibration excited stator vines is due to interaction between turbine wheel and stator vines. As a result spinning turbine wheel oscillated with mode 7 diameters.

Influence of permeable beds on hydraulically macro-rough flow

In this study, macro-rough flows over beds with different permeability values are simulated using the large-eddy simulation, and the results are analysed by applying the double-averaging (DA) methodology. Spheres of different sizes and arrangements were used to form the beds, which are deemed to be permeable granular beds. The influence of bed permeability on the turbulence dynamics and structure is investigated. It was observed that the scales of the spanwise vortical structures over more permeable beds are larger than those over less permeable beds. This is attributed to large-scale spanwise-alternate strips of varying Reynolds shear stress (RSS), emerging from the surface of macro-rough elements for the permeable beds. The DA stress balance suggests that the time-averaged spanwise vortical structure leads to a damping in DA RSS and an unusual peak of the form-induced stress in the main flow. In the streamwise direction, both large turbulent structures that originate from the Kelvin–Helmholtz-type instability and small turbulent structures that are associated with the turbulent transport across the gaps of the roughness elements are more prevalent over highly permeable beds. Near the bed, the relative magnitude of turbulent events shows a transition from a ejections-dominating to sweeps-dominating zone with vertical distance. Further, several hydrodynamic characteristics normalized by inner scales (kinematic viscosity to shear velocity ratio) show a greater dependency on permeability Reynolds number than those normalized by sediment size. The study provides an insight into the mechanism of mass transfer near the fluid–particle interface, which is vital to benthic and aquatic ecology.

Constructing highly oriented segregated structure towards high-strength carbon nanotube/ultrahigh-molecular-weight polyethylene composites for electromagnetic interference shielding

Formation of segregated structure in the conductive polymer composites remarkably improves electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE), however suffers from the deteriorated mechanical performance due to the poor interfacial interaction between the polymer granules. Herein, solid phase extrusion (SPE) was used to prepare mechanically strong carbon nanotube/ultrahigh-molecular-weight polyethylene composites with highly oriented segregated structure. The tensile strength of SPE composites was significantly enhanced to a considerable level of ∼100 MPa, 178% higher than the conventional compression-molded (CM) counterparts (∼36 MPa). It was attributed to the structure orientation induced by the shear flow and compacted granule adhesion facilitated by the high extrusion pressure of SPE. Moreover, SPE composites displayed the comparable electrical conductivity and EMI SE to the CM samples. Besides, an unusual resonance peak appeared on the EMI SE curves for SPE samples due to the special segregated structure, giving a hint of selective EMI shielding.

Observation and explanation of two-dimensional interconversion of oximes with multiple heart-cutting using comprehensive multidimensional gas chromatography

Real-time interconversion processes produce unconventional peak broadening in gas chromatography (GC), and can be used to generate kinetic and thermodynamic data. In this study, an unusual separation situation in comprehensive two dimensional GC where two dimensional interconversion (i.e. a raised plateau in both first and second dimension, 1D and 2D) was observed in analysis of oxime isomers. This resulted in a characteristic and unusual rectangular peak shape in the two dimensional result. A related theoretical approach was introduced to explain the peak shape supported by simulation results which can be varied depending on concentration profiles and kinetics of the process. The simulated results were supported by experimental results obtained by a comprehensive heart-cut multidimensional GC (H/C MDGC) approach which was developed to clearly investigate isomerisation of E/Z oxime molecules in both 1D and 2D separations under different isothermal conditions. The carrier gas flow and oven temperature were selected according to initial results for 1D interconversion on a poly(ethyleneglycol) stationary phase, which was further used in both 1D and 2D separations to result in broad zones of oxime interconversion in both dimensions. The method involved repetitive injections of oxime sample, then sampling contiguous fractions of sample into a long 2D column which is intended to promote considerable interconversion. Comprehensiveness arises from the fact that the whole sample is sampled from the 1D to the 2D column, with the long 2D column replacing the short 2D column used in classical comprehensive two-dimensional gas chromatography, where the latter will not promote sufficient interconversion. Data processing and presentation permits a ‘rectangular’ distribution corresponding to the separated compounds, characteristic of this experiment.

OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-peak Gravitational Microlensing Event

Abstract We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits five very unusual peaks, four of which were produced by caustic crossings and the other by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax π E . Furthermore, the three resolved caustics allow us to measure the angular Einstein radius θ E . From the combination of π E and θ E , the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses M 1 = 0.52 ± 0.04 M ⊙ and M 2 = 0.42 ± 0.03 M ⊙ separated in projection by a ⊥ = 6.4 ± 0.5 au . The lens is located in the disk with a distance of D L = 3.3 ± 0.3 kpc . The reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.

Structural studies of the high temperature phases of AgTaO3

The temperature dependence of the structure of a polycrystalline sample of AgTaO3 has been determined using in-situ Synchrotron X-ray powder diffraction methods. This work finds no evidence for the presence of a monoclinic phase, rather three phase transitions have been identified, namely R3c↔390°CCmcm↔465°CP4/mbm↔580°CPm3̅m. The rhombohedral phase was further studied at room temperature by neutron powder diffraction. The co-existence of the rhombohedral and orthorhombic phases around 380–400 ° C indicates that the transition between these is first order, and gives rise to unusual peak shapes in the diffraction patterns.

Study of Perfluoroalkyl Chain-Specific Band Shift in Infrared Spectra on the Chain Length.

The CF2 symmetric stretching vibration (νs(CF2)) band of a perfluoroalkyl (Rf) group in an infrared (IR) spectrum exhibits a unique character, that is, an apparent high wavenumber shift with increasing the chain length, which is an opposite character to that of the CH stretching vibration band of a normal alkyl chain. To reveal the mechanism of the unusual IR band shift, two vibrational characters of an Rf chain are focused: (1) a helical conformation of an Rf chain, (2) the carbon (C) atoms having a smaller mass than the fluorine (F) atom dominantly vibrate as a coupled oscillator leaving F atoms stay relatively unmoved. These indicate that a "coupled oscillation of the skeletal C atoms" of an Rf chain should be investigated considering the helical structure. In the present study, therefore, the coupled oscillation of the Rf chain dependent on the chain length is investigated by Raman spectroscopy, which is suitable for investigating a skeletal vibration. The Raman-active νs(CF2) band is found to be split into two bands, the splitting is readily explained by considering the helical structure and length with respect to group theory, and the unusual peak shift is concluded to be explained by the helical length.

The curious case of cuprous chloride: Giant thermal resistance and anharmonic quasiparticle spectra driven by dispersion nesting

Strongly anharmonic phonon properties of CuCl are investigated with inelastic neutron-scattering measurements and first-principles simulations. An unusual quasiparticle spectral peak emerges in the phonon density of states with increasing temperature, in both simulations and measurements, emanating from exceptionally strong coupling between conventional phonon modes. Associated with this strong anharmonicity, the lattice thermal conductivity of CuCl is extremely low and exhibits anomalous, nonmonotonic pressure dependence. We show how this behavior arises from the structure of the phonon dispersions augmenting the phase space available for anharmonic three-phonon scattering processes, and contrast this mechanism with common arguments based on negative Gr\"uneisen parameters. These results demonstrate the importance of considering intrinsic phonon-dispersion structure toward understanding scattering processes and designing new ultralow thermal conductivity materials.