Field Induced Spin Density Wave Research Articles

Compass-like manipulation of electronic nematicity in Sr3Ru2O7

Electronic nematicity has been found in a wide range of strongly correlated electron materials, resulting in the electronic states having-4.5pc]Please note that the spelling of the following author name(s) in the manuscript differs from the spelling provided in the article metadata: Izidor Benedičič. The spelling provided in the manuscript has been retained; please confirm. a symmetry that is lower than that of the crystal that hosts them. One of the most astonishing examples is [Formula: see text], in which a small in-plane component of a magnetic field induces significant resistivity anisotropy. The direction of this anisotropy follows the direction of the in-plane field. The microscopic origin of this field-induced nematicity has been a long-standing puzzle, with recent experiments suggesting a field-induced spin density wave driving the anisotropy. Here, we report spectroscopic imaging of a field-controlled anisotropy of the electronic structure at the surface of [Formula: see text]. We track the electronic structure as a function of the direction of the field, revealing a continuous change with the angle. This continuous evolution suggests a mechanism based on spin-orbit coupling resulting in compass-like control of the electronic bands. The anisotropy of the electronic structure persists to temperatures about an order of magnitude higher compared to the bulk, demonstrating novel routes to stabilize such phases over a wider temperature range.

Helical and collinear spin density wave order in the S=12 one-dimensional frustrated chain compound NaCuMoO4(OH) investigated by neutron scattering

We performed neutron diffraction experiments on a single crystal of an $S=\frac{1}{2}$ frustrated ferromagnetic chain compound ${\mathrm{NaCuMoO}}_{4}$(OH) at zero and finite magnetic fields. Three magnetic Bragg peaks with the propagation vector of $\mathbit{q}=(0,\ensuremath{\delta},0)$ $[\ensuremath{\delta}=0.481(1)]$ were observed at the zero field, which means that an incommensurate helical magnetic order was realized. Using the ratio of the intensities between these magnetic peaks, a proper-screw structure was suggested, where the spiral plane is the crystallographic $ac$ plane. While the $\ensuremath{\delta}$ is unchanged at lower fields, it decreases linearly with the field where ${\ensuremath{\mu}}_{0}H\ensuremath{\ge}2.5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The field dependence is consistent with that of the field-induced spin density wave state that originated from the formation of the bound state of two magnons in the $S=\frac{1}{2}$ frustrated ferromagnetic chain.

Unconventional field-induced spin density wave phases in quasi-one-dimensional conductors in high magnetic fields

It is known that the Field-Induced Spin-Density-Wave (FISDW) phases are experimentally observed in the quasi-one-dimensional (Q1D) organic conductors with chemical formula (TMTSF)$_2$X (X=PF$_6$, ClO$_4$, etc.) and some others in moderate magnetic fields. From a theoretical point of view, they appear as a result of "one-dimensionalization" of the Q1D electron spectra due to the orbital electron effect in a magnetic field. We predict that the novel FISDW phases with different physical meaning have to appear in inclined high magnetic fields in Q1D conductors as a result of combination of the spin-splitting and orbital electron effects. We suggest performing the corresponding experiments in the (TMTSF)$_2$X materials.

Field-induced spin-density wave beyond hidden order in URu2Si2.

URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations.

Role of anion ordering and effective pressure in the field-induced spin-density-wave phase of (TMTSF)2X

Magnetoresistance and Hall resistance measurements were conducted in the field-induced spin-density-wave (FISDW) phase of (TMTSF)2ReO4 above 1.0 GPa, with an anion ordering specified by . The quantized Hall resistance shows the sequence , with decreasing field that is successfully explained by the “extended standard model”. Consequently, we demonstrate that the difference between the chemical and hydrostatic pressures is linked to the appearance of the peculiar FISDW phase of the TMTSF salts with .

Interplay between spin-density wave and 3d local moments with random exchange in a molecular conductor

We present the results of high-pressure transport measurements on the anion-mixed molecular conductors (DIETSe)${}_{2}M{\mathrm{Br}}_{2}{\mathrm{Cl}}_{2}$ [DIETSe = diiodo(ethylenedithio)tetraselenafulvalene; $M=\mathrm{Fe}$, Ga]. They undergo a metal-insulator (M-I) transition below 9 K at ambient pressure, which is suppressed by applying pressure, indicating a spin-density-wave (SDW) transition caused by a nesting instability of the quasi-one-dimensional (Q1D) Fermi surface, as observed in the parent compounds (DIETSe)${}_{2}M{\mathrm{Cl}}_{4}$ ($M=\mathrm{Fe}$, Ga). In the metallic state, the existence of the Q1D Fermi surface is confirmed by observing the Lebed resonance. The critical pressures of the SDW, ${P}_{\mathrm{c}}$, of the $M{\mathrm{Br}}_{2}{\mathrm{Cl}}_{2}$ ($M=\mathrm{Fe}$, Ga) salts are significantly lower than those of the the $M{\mathrm{Cl}}_{4}$ ($M$ = Fe, Ga) salts, suggesting chemical pressure effects. Above ${P}_{\mathrm{c}}$, field-induced SDW transitions appear, as evidenced by kink structures in the magnetoresistance (MR) in both salts. The ${\mathrm{FeBr}}_{2}{\mathrm{Cl}}_{2}$ salt also shows antiferromagnetic (AF) ordering of $d$ spins at 4 K, below which significant spin-charge coupling is observed. A large positive MR change up to 150% appears above the spin-flop field at high pressure. At low pressure, in particular below ${P}_{\mathrm{c}}$, a dip or kink structure appears in MR at the spin-flop field, which shows unconventionally large hysteresis at low temperature $(T<1$ K). The hysteresis region clearly decreases with increasing pressure towards ${P}_{\mathrm{c}}$, strongly indicating that the coexisting SDW plays an important role in the enhancement of magnetic hysteresis besides the random exchange interaction.

Topological phase transition in quasi-one dimensional organic conductors.

We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane’s model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices.

Field-induced spin density wave and spiral phases in a layered antiferromagnet

We determine the low-field ordered magnetic phases of the $S=1$ dimerized antiferromagnet ${\mathrm{Ba}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{8}$ using single-crystal neutron diffraction. We find that for magnetic fields between ${\ensuremath{\mu}}_{0}H=8.80\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ and $10.56\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ applied along the $[1\overline{1}0]$ direction the system exhibits spin density wave order with incommensurate wave vectors of type $(\ensuremath{\eta},\ensuremath{\eta},\ensuremath{\epsilon})$. For ${\ensuremath{\mu}}_{0}Hg10.56\phantom{\rule{0.28em}{0ex}}\mathrm{T}$, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the $[hh0]$ direction. For both field-induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. The nature of these two transitions is fundamentally different: the low-field transition is a second-order transition to a spin density wave ground state, while the one at higher field, toward the spiral phase, is of first order.

Hofstadter butterflies and quantized Hall conductance in quasi-one dimensional organic conductors

We explore the structure of the energy spectra of quasi-one dimensional organic conductors subjected to the field-induced spin-density-wave (FISDW) state. We show that the structure of the energy spectra can exhibit Hofstadter butterfly, which is generally believed to appear in two dimensional systems. The phenomenon of the quantized Hall conductance due to FISDW is also investigated. We find that the Hall number L, which is defined by L = σxy/(e2/h), coincides with the number described by FISDW order parameter. The sign reversal of the quantized Hall conductance is discussed theoretically.

Magnetic-field-induced phase transitions in the quasi-one-dimensional organic conductor HMTSF–TCNQ

Motivated by an interest to see if the field-induced (FI) phase in the charge-density wave (CDW) system is similar to the field-induced-SDW (FISDW) in (TMTSF)2X, (TMTSF: tetramethyltetraselenafulvalene), we examined the magnetic-field-induced phases in a quasi-one-dimensional (Q1D) organic conductor HMTSF–TCNQ (hexamethylene- tetraselenafulvalene- tetracyanoquinodimethane) under a pressure of 1.1 GPa, where the CDW occurring at 30 K is suppressed. The work was carried out by measurements of angular-dependent magnetoresistance oscillations and exploratory work on the Hall effect. It turned out that the FI-phase, most likely a FICDW for B > 0.1 T, accompany a quantum Hall effect, and the FI-phase transitions are controlled by the field component along the least conducting axis. Above 10 T, the lowest Landau level of the small 2D Fermi pocket (due to incomplete nesting of Fermi surface) exceeds the Fermi level, reaching the quantum limit. Although there are many differences between the CDW (HMTSF–TCNQ) and SDW ((TMTSF)2X) systems, a similar scenario for field-induced phases seems to hold.

Excitations and quasi-one-dimensionality in field-induced nematic and spin density wave states

We study the excitation spectrum and dynamical response functions for several quasi-one-dimensional spin systems in magnetic fields without dipolar spin order transverse to the field. This includes both nematic phases, which harbor "hidden" breaking of spin-rotation symmetry about the field and have been argued to occur in high fields in certain frustrated chain systems with competing ferromagnetic and antiferromagnetic interactions, and spin density wave states, in which spin-rotation symmetry is truly unbroken. Using bosonization, field theory, and exact results on the integrable sine-Gordon model, we establish the collective mode structure of these states, and show how they can be distinguished experimentally.

Anomalous magnetoresistance and hidden spin canting in (DIETSe)2MCl4(M=Fe, Ga)

The quasi-one-dimensional (Q1D) molecular conductors (DIETSe)${}_{2}$$M$Cl${}_{4}$ [$M=\text{Fe}$, Ga] undergo a spin density wave (SDW) transition below 12 K. The SDW ground state is suppressed by applying high pressure, recovering the Q1D Fermi surface which is confirmed by the appearance of Lebed resonance in the angle-dependent magnetoresistance (MR). Above the critical pressure of SDW, MR shows kink structures at high magnetic fields, reminiscent of field-induced spin density wave (FISDW) transition in both salts. The $\ensuremath{\pi}$-$d$ hybrid (DIETSe)${}_{2}$FeCl${}_{4}$ also exhibits an antiferromagnetic (AF) transition of $d$-electron spins at 2.5 K, below which the spin-flop-induced positive large MR are observed. The change in the interlayer MR reaches 130$%$ at 10.5 kbar. The resistance anomalies associated with spin flop are also observed in the angle-dependent MR at low magnetic fields below 5 T, associated with clear hysteresis. A polar plot of these anomalies reveals the presence of hidden spin canting. Two magnetic easy axes of $d$-electron spins are found to be tilted $\ifmmode\pm\else\textpm\fi{}$16 degrees from the $b$ axis towards the $c$ axis. The interplay between the SDW instability of Q1D $\ensuremath{\pi}$ electrons and the local moments of AF $d$-electron spins is considered as the origin of the anomalous transport behaviors.

Field-Induced CDW Phases in a Quasi-One-Dimensional Organic Conductor, HMTSF-TCNQ Under Pressure of 1 GPa in Magnetic Field of 31 T

HMTSF-TCNQ is a quasi-one-dimensional organic conductor which undergoes CDW(charge density wave) transition at 30 K at ambient pressure, where HMTSF-TCNQ is hexamethylenetetraselena fulvalene-tetracyano quino dimethane. This CDW is suppressed by the pressure of 1 GPa. At this pressure, we found field-induced successive hysteretic transitions in magnetoresistance. This reminds us of the successive field-induced SDW (spin density wave) phases in TMTSF2X salts. However, the field range of interest is 2–3 times higher than that of TMTSF2X salts. Therefore, we need really high field to examine these properties. It is very likely that the field induced phases are of field induced CDW (FICDW), where quantum Hall effect and many interesting phenomena are expected like in the case of FISDW. Together with the magnetoresistance study up to the field of 31 Tesla and at temperatures down to 0.4 K in various magnetic field angles respective to the crystal axes, we examined the angular dependence of magnetoresistance oscillations(AMRO). It turned out that AMRO demonstrates clearly the occurrence of field-induced phase rather than the magneto-resistance by field sweep. Since the Hall resistance, R xy in the field-induced phases showed stepwise plateau structure against the field sweep, and its strength was in the order of magnitude of h/e 2 per molecular sheet, the Hall effect is very suggestive of quantum Hall effect.

Field-induced CDW in HMTSF-TCNQ

Field-induced successive transitions were observed in magnetoresistance in the quasi-one-dimensional organic conductor, HMTSF-TCNQ, hexamethylene-tetraselena-fulvalene-tetracyanoquinodimethane. The magnetoresistance exhibits kink transitions accompanying hysteresis at pressures around 1GPa, but neither at p=0 nor at 2GPa. At p=0 and below 30K, this material undergoes charge density wave (CDW) state, which is suppressed around 1GPa, where successive transitions are observed. Since these behavior is only observed at the boundary in pressure between insulator and metal, and the nature of the insulating state is CDW at p=0, it is strongly suggested that the successive transitions observed in magnetoresistance might be associated with CDW, accordingly a field-induced CDW by the one-dimensionalization by strong magnetic field ranging from 10 to 30T. The behaviors are compared with previously claimed FICDW and the established FISDW (field-induced-spin-density-wave).

Theory of an inherent spin-density-wave instability due to vortices in superconductors with strong Pauli effects

A novel spin density wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low temperature (HL) phase in CeCoIn$_5$. In the vortex state the strong Pauli effect and the nodal gap conspire to enhance the momentum resolved spectral weight exclusively along the nodal direction over the normal value, providing a favorable nesting condition for SDW with ${\bf Q}=(2k_F, 2k_F, 0.5)$ only under high field ($H$). Observed mysteries of the field-induced SDW confined within $H_{c2}$ are understood consistently, such facts that ${\bf Q}$ is directed to the nodal direction independent of $H$, SDW diminishes under tilting field from the $ab$ plane, and the SDW transition line in $(H,T)$ has a positive slope.

Field-Induced Successive Phase Transitions in the Charge Density Wave Organic Conductor HMTSF-TCNQ

The magnetoresistance of quasi-1D two-chain organic conductor HMTSF-TCNQ (hexamethylenetetraselenafulvalene-tetracyanoquinodimethane), which shows charge density wave transition at ambient pressure, was studied under pressure up to 27 T and 31 T, in two high field facilities. We found a kink structure in the magnetoresistance reminiscent of field-induced spin density wave at an intermediate pressure of 1.5 GPa between 0 and 2 GPa. We speculate that these are successive quantum phases induced by magnetic field.

Nesting of the Fermi surface and the wave-vector-dependent susceptibility in quasi-one-dimensional electron systems

The wave-vector dependence of the susceptibility in quasi-one-dimensional systems is studied theoretically without and with external magnetic field in the perpendicular direction. We show that the wave-vector-dependent susceptibility has a two-step plateaulike structure in the absence of the magnetic field, when the warping of the Fermi surface caused by the $\ensuremath{\mp}2{\ensuremath{\tau}}_{3}\text{ }\text{sin}[3({k}_{y}\ensuremath{\mp}\ensuremath{\phi})]$ term, which breaks the reflection symmetry with respect to the most conducting chain, is larger than the critical value. The susceptibility is shown to have the plateaulike maximum in the small region in the wave vector at the edge of the lower plateau. We discuss the importance of the plateaulike maximum for the the field-induced spin density wave states in quasi-one-dimensional systems, such as the organic conductors ${(\text{TMTSF})}_{2}{\text{PF}}_{6}$ and ${(\text{TMTSF})}_{2}{\text{ClO}}_{4}$.

Generalized susceptibility of the quasi-one-dimensional organic conductors with the triclinic lattice symmetry

The instability of the field-induced spin density wave states of the quasi-one-dimensional system is studied by using the model including the triclinic lattice symmetry and multi-transfer integrals. By calculating the magnetic susceptibility χ 0 ( Q ) , we found the asymmetric sweptback peak at q x – q y plane contrary to the symmetric peak for the model with the square lattice symmetry and single transfer integral.

Phase diagram of the field-induced spin density wave state in [formula omitted] deduced from the specific heat measurements

We have measured the specific heat of the quasi-one dimensional organic conductor ( TMTSF ) 2 ClO 4 . The clear phase diagram of the field-induced spin density wave state was obtained from the density plot of the specific heat. We observed the reentrance to the metallic state and the tetracritical behavior quite clearly, though there is no evidence of the ”tree-like” structure.

Vortex states in iron-based superconductors with collinear antiferromagnetic cores

Magnetism in the FeAs stoichiometric compounds and its interplay with superconductivity in vortex states are studied by self-consistently solving the Bogoliubov-de Gennes equations based on a two-orbital model with including the on-site interactions between electrons in the two orbitals. It is revealed that for the parent compound, magnetism is caused by the strong Hund's coupling, and the Fermi-surface topology aids to select the spin-density-wave (SDW) pattern. The superconducting (SC) order parameter with ${s}_{\ifmmode\pm\else\textpm\fi{}}={\ensuremath{\Delta}}_{0}\text{ }\text{cos}({k}_{x})\text{cos}({k}_{y})$ symmetry is found to be the most favorable pairing for both the electron- and hole-doped cases while the local density of states exhibits the characteristic of nodal gap for the former and full gap for the latter. In the vortex state, the emergence of the field-induced SDW depends on the strength of the Hund's coupling and the Coulomb repulsions. The field-induced SDW gaps the finite-energy contours on the electron- and hole-pocket sides, leading to the dual structures with one reflecting the SC pairing and the other being related to the SDW order. These features can be discernable in STM measurements for identifying the interplay between the field-induced SDW order and the SC order around the core region.