Function Of Uniaxial Stress Research Articles

Uniaxial stress effect on the electronic structure of quantum materials

Uniaxial stress has proven to be a powerful experimental tuning parameter for effectively controlling lattice, charge, orbital, and spin degrees of freedom in quantum materials. In addition, its ability to manipulate the symmetry of materials has garnered significant attention. Recent technical progress to combine uniaxial stress cells with quantum oscillation and angle-resolved photoemission techniques allowed to study the electronic structure as function of uniaxial stress. This review provides an overview on experimental advancements in methods and examines studies on diverse quantum materials, encompassing the semimetal WTe2, the unconventional superconductor Sr2RuO4, Fe-based superconductors, and topological materials.

Nematic quantum criticality in an Fe-based superconductor revealed by strain-tuning.

Quantum criticality may be essential to understanding a wide range of exotic electronic behavior; however, conclusive evidence of quantum critical fluctuations has been elusive in many materials of current interest. An expected characteristic feature of quantum criticality is power-law behavior of thermodynamic quantities as a function of a nonthermal tuning parameter close to the quantum critical point (QCP). Here, we observed power-law behavior of the critical temperature of the coupled nematic/structural phase transition as a function of uniaxial stress in a representative family of iron-based superconductors, providing direct evidence of quantum critical nematic fluctuations in this material. These quantum critical fluctuations are not confined within a narrow regime around the QCP but rather extend over a wide range of temperatures and compositions.

Elastic properties of two VTI shale samples as a function of uniaxial stress: Experimental results and application of the porosity-deformation approach

Shale is a complex medium composed of clay, other mineral phases, and a pore space. The combined elastic properties of these components control the effective (anisotropic) properties of the composite solid. The factor that is the most dependent on the stress field is the structure of the pore space, which greatly influences the elastic properties of the medium. We have further developed and experimentally validated the porosity deformation approach (PDA) for understanding and modeling stress-dependent changes of the elastic properties of sedimentary rocks. PDA separates the pore space into stiff and compliant parts. The load dependencies of the elastic properties have linear contributions due to the former and exponential contributions due to the latter. We evaluate data sets of elastic properties of two vertical transverse isotropic shale samples measured under uniaxial stress. Then we apply the PDA and our optimization algorithm to the measured data sets to model the stress dependency of the seismic velocities and validate the modeling with experimentally obtained results. We have developed for the first time the constant anellipticity approach (CAN), which estimates the off-axis velocity (in an inclined direction relative to the symmetry axis direction) as a function of stress. Measurements of off-axis velocities are often missing information, and CAN permits us to fill this gap. This provides further background for the reconstruction of the stress dependency of the compliance tensor from acoustic log data.

Optical anisotropy in the electronic nematic phase of FeSe

At ambient pressure, FeSe undergoes a structural, tetragonal-to-orthorhombic, phase transition at ${T}_{s}\ensuremath{\simeq}90$ K without any magnetic ordering on further cooling. FeSe thus provides an arena for examining the nematic phase without the complications following the reconstruction of the Fermi surface due to the antiferromagnetic order within the orthorhombic state. We perform an optical-reflectivity investigation across the structural transition, as a function of uniaxial stress in order to detwin the specimen. These measurements reveal a hysteretic behavior of the anisotropic optical response to uniaxial stress for $T\ensuremath{\le}{T}_{s}$, which extends to energy scales of about 0.5 eV. The sign changes of the optical anisotropy between distinct energy intervals suggest a complex evolution of the polarized electronic structure in the nematic phase. The temperature dependence of the optical anisotropy for the fully detwinned specimen is furthermore acting as a proxy for the order parameter of nematicity.

Electrodynamic response in the electronic nematic phase ofBaFe2As2

We perform, as a function of uniaxial stress, a temperature-dependent optical-reflectivity investigation of the parent Fe-arsenide compound ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ over a broad spectral range, from the far infrared up to the ultraviolet, across the coincident structural tetragonal-to-orthorhombic and spin-density-wave (SDW) phase transitions at ${T}_{s,N}=135$ K. Our results provide knowledge to the complete electrodynamic response of the title compound over a wide energy range as a function of both tunable variables. For temperatures below ${T}_{s,N}$, varying the uniaxial stress in situ affects the twin domain population and yields hysteretic behavior of the optical properties as the stress is first increased and then decreased, whereas for temperatures above ${T}_{s,N}$ the stress-induced optical anisotropy is reversible, as anticipated. In particular, by analyzing the low-frequency infrared response, we obtain detailed insight to the effects determining the intrinsic anisotropy of the (metallic) charge dynamics in the orthorhombic state, and similarly the induced one due to applied uniaxial stress at higher temperatures in the tetragonal phase. The low-frequency optical conductivity thus allows establishing a link to the $dc$ transport properties and reveals that they are determined almost exclusively by changes in the Drude weight, therefore by the anisotropy in the Fermi surface parameters. Finally, we show that the spectral weight distribution in the SDW state occurs for energies below approximately 1 eV, and therefore points towards a correlation mechanism due to Hund's coupling rather than on-site Coulomb interactions.

Origin of the Resistive Anisotropy in the Electronic Nematic Phase of BaFe(2)As(2) Revealed by Optical Spectroscopy.

We perform, as a function of uniaxial stress, an optical-reflectivity investigation of the representative "parent" ferropnictide BaFe(2)As(2) in a broad spectral range, across the tetragonal-to-orthorhombic phase transition and the onset of the long-range antiferromagnetic (AFM) order. The infrared response reveals that the dc transport anisotropy in the orthorhombic AFM state is determined by the interplay between the Drude spectral weight and the scattering rate, but that the dominant effect is clearly associated with the metallic spectral weight. In the paramagnetic tetragonal phase, though, the dc resistivity anisotropy of strained samples is almost exclusively due to stress-induced changes in the Drude weight rather than in the scattering rate, definitively establishing the anisotropy of the Fermi surface parameters as the primary effect driving the dc transport properties in the electronic nematic state.

Terahertz-range spontaneous emission under the optical excitation of donors in uniaxially stressed bulk silicon and SiGe/Si heterostructures

The results of measurements of the total terahertz-range photoluminescence of Group-V donors (phosphorus, antimony, bismuth, arsenic) in bulk silicon and SiGe/Si heterostructures depending on the excitation intensity are presented. The signal of bulk silicon was also measured as a function of uniaxial stress. The results of measurement of the dependence of the spontaneous emission intensity on the uniaxial stress is in rather good agreement with theoretical calculations of the relaxation times of excited states of donors in bulk silicon. Comparative measurements of the spontaneous emission from various strained heterostructures showed that the photoluminescence signal is caused by donor-doped silicon regions.

Notes on Anderson localization

Ad Lagendijk, Bart van Tiggelen, and Diederik Wiersma, in their article “Fifty years of Anderson localization” (PHYSICS TODAY, August 2009, page 24), discuss the experimental studies in semiconductors such as weakly compensated phosphorus-doped silicon. However, the authors don’t accurately depict the situation, and they ignore important work.Lagendijk and coauthors note that in 1982 a Bell Labs group11. M. A. Paalanen, T. F. Rosenbaum, G. A. Thomas, R. N. Bhatt, Phys. Rev. Lett. 48, 1284 (1982). https://doi.org/10.1103/PhysRevLett.48.1284 found that for charge-carrier densities n above a critical value nc in weakly compensated Si:P, the conductivity, extrapolated to zero temperature, scaled with reduced density with an exponent s of approximately 0.5; for compensated semiconductors (also amorphous alloys), experiments yielded s of approximately 1, which agrees with the scaling theory. As the authors describe, that finding led to the “exponent puzzle.” But the zero-compensation case includes only off-diagonal order in contrast to the 1958 paper by Philip Anderson. The different disorder cases are characterized by different scaling exponents.Considerable controversy ensued in 1993–99. H. Stupp at Karlsruhe University and coauthors22. H. Stupp, M. Hornung, M. Lakner, O. Madel, H. von Löhneysen, Phys. Rev. Lett. 71, 2634 (1993); https://doi.org/10.1103/PhysRevLett.71.2634 T. Castner, Phys Rev. Lett. 73, 3600 (1994) https://doi.org/10.1103/PhysRevLett.73.3600 claimed an exponent of 1.3 for Si:P, but with nc 6% lower than the Bell group. I showed that for n between 3.52 × 1018 cm−3 and 3.69 × 1018 cm−3, the data were a better fit to Mott variable-range hopping; the finding suggests that these samples were insulating as T → 0. A 6% decrease in nc increased s from 0.5 to 1.3, which demonstrates the very strong coupling between s and nc. Lagendijk and coauthors state, without giving references, “In 1999, researchers argued that an exponent of 1 is recovered in the experiments on silicon if the conductivity is correctly extrapolated to zero temperature.” That statement is misleading. In 1999 two groups33. S. Bogdanovich, M. P. Sarachik, R. N. Bhatt, Phys. Rev. Lett. 82, 137 (1999); https://doi.org/10.1103/PhysRevLett.82.137S. Waffenschmidt, C. Pfleiderer, H. von Löhneysen, Phys. Rev. Lett. 83, 3005 (1999). https://doi.org/10.1103/PhysRevLett.83.3005 reported measurements of σ as a function of uniaxial stress on Si:B and Si:P. Both groups observed a substantial increase in s from near 0.5 to between 1.2 and 1.5 close to nc. However, compressive uniaxial stress introduces inhomogeneity from sample bending, which increases s.44. T. G. Castner, Phys. Rev. Lett. 87, 129701 (2001). https://doi.org/10.1103/PhysRevLett.87.129701 The features of the 1999 data were similar to the Bell Si:P data, but the Bell group didn’t analyze the tail portion of its data very close to nc where the stress inhomogeneity became dominant and σ is small.Are features like weak localization or carrier interactions relevant or essential to explain the scaling component of approximately 0.5 for the weakly compensated case? Although there may still be disagreement, some researchers believe the answer is no. Two different calculations, both featuring the two-component model, yield σ ∝ kF, the Fermi wavevector, and kF ∝ (EF − Ec)1/2 for noninteracting carriers. That explanation is consistent with a Boltzmann–Drude conductivity.55. J. C. Phillips, Phys Rev. B 45, 5863 (1992); https://doi.org/10.1103/PhysRevB.45.5863 T. G. Castner, Phys. Rev. Lett. 84, 1539 (2000). https://doi.org/10.1103/PhysRevLett.84.1539 Since kF = 2π/λdB, with λdB the de Broglie wavelength, the calculations demonstrate a second scaling length besides the ubiquitous correlation length ξ(n). Those explanations were ignored by Lagendijk and coauthors.REFERENCESSection:ChooseTop of pageREFERENCES <<1. M. A. Paalanen, T. F. Rosenbaum, G. A. Thomas, R. N. Bhatt, Phys. Rev. Lett. 48, 1284 (1982). https://doi.org/10.1103/PhysRevLett.48.1284 , Google ScholarCrossref, CAS2. H. Stupp, M. Hornung, M. Lakner, O. Madel, H. von Löhneysen, Phys. Rev. Lett. 71, 2634 (1993); https://doi.org/10.1103/PhysRevLett.71.2634 , Google ScholarCrossref, CAST. Castner, Phys Rev. Lett. 73, 3600 (1994) https://doi.org/10.1103/PhysRevLett.73.3600 , , Google ScholarCrossref, CAS3. S. Bogdanovich, M. P. Sarachik, R. N. Bhatt, Phys. Rev. Lett. 82, 137 (1999); https://doi.org/10.1103/PhysRevLett.82.137, Google ScholarCrossref, CASS. Waffenschmidt, C. Pfleiderer, H. von Löhneysen, Phys. Rev. Lett. 83, 3005 (1999). https://doi.org/10.1103/PhysRevLett.83.3005, , Google ScholarCrossref, CAS4. T. G. Castner, Phys. Rev. Lett. 87, 129701 (2001). https://doi.org/10.1103/PhysRevLett.87.129701 , Google ScholarCrossref, CAS5. J. C. Phillips, Phys Rev. B 45, 5863 (1992); https://doi.org/10.1103/PhysRevB.45.5863 , Google ScholarCrossref, CAST. G. Castner, Phys. Rev. Lett. 84, 1539 (2000). https://doi.org/10.1103/PhysRevLett.84.1539 , , Google ScholarCrossref, CAS© 2012 American Institute of Physics.

Atomistic considerations of stressed epitaxial growth from the solid phase

A dual-timescale model of stressed solid-phase epitaxial growth is developed to provide a basis for the atomistic interpretation of experiments where the macroscopic growth velocity of (0 0 1) Si was studied as a function of uniaxial stress applied in the plane of the growth interface. The model builds upon prior empirical modeling, but is a significant improvement as it provides solid physical bases as to the origin of growth being dual-timescale and more accurately models growth kinetics.

In situ neutron diffraction under tensile loading of powder-in-tube Cu∕Nb3Sn composite wires: Effect of reaction heat treatment on texture, internal stress state, and load transfer

The strain induced degradation of Nb3Sn superconductors can hamper the performance of high field magnets. The authors report elastic strain measurements in the different phases of entire non-heat treated and fully reacted Nb3Sn composite strands as a function of uniaxial stress during in situ deformation under neutron beam. After the reaction heat treatment the Cu matrix loses entirely its load carrying capability and the applied stress is transferred to the remaining Nb–Ta alloy and to the brittle (Nb–Ta)3Sn phase, which exhibits a preferential ⟨110⟩ grain orientation parallel to the strand axis.

Influence of Uniaxial Stress on the Polarization of Spontaneous Emission from p-Ge

The intensity of polarized spontaneous emission as a function of uniaxial stress in p-Ge is studied. It is found that with rising of stress dependence of the radiation polarization rotates by π/2. The effect is explained by the modification of the energy spectrum of free and impurity states under the uniaxial compression.

Uniaxial stress dependence of the binding energy of shallow donor impurities in GaAs–(Ga,Al)As quantum dots

We have studied the effects of an uniaxial stress on the binding energy of a shallow donor impurity in a parallelepiped-shaped GaAs–(Ga,Al)As quantum dot. In the calculations we have used a variational technique within the effective-mass approximation. The stress was applied in the z direction and the donor impurity was located at various positions along the z axis. Our results show that the donor binding energy increases with increasing stress and for decreasing sizes of the quantum dot. Also, we have found that the binding energy for various values of the donor position along the z axis for constant quantum well box size increases with the proximity of the impurity to the center of the structure. Moreover, we obtain the shallow-donor binding energies as functions of uniaxial stress in the limit in which the quantum dot turns into either a quantum well or a quantum-well wire.

Coercive force of low-carbon steels as a function of uniaxial stress. Part I

Analytical functions describing variations in the coercive force measured along and across the axis of tensile stress versus the stress magnitude taking into account changes in domain dimensions are given. The formulas have been tested for low-carbon steels.

Effects of uniaxial stress on the piezoelectric, dielectric, and mechanical properties of lead zirconate titanate piezoceramics

Piezoelectric ceramics are often used under compressive stress. It is therefore important to know the properties of these materials as a function of applied stress. We have developed an experiment that allows us to find the piezoelectric charge coefficient d33, elastic compliance SE 33, and dielectric constant ϵT 33 as a function of uniaxial stress in the poled direction. Both dynamic and static measurements can be carried out. The dynamic and static coefficients differ from each other because of the different proportions of reversible and irreversible domain changes that contribute to them and each coefficient can be important in specific applications. Dynamic results for stresses up to 160 MPa on a soft and a hard piezoelectric Lead Zirconate Titanate (PZT) ceramics are presented. The time dependence of the measurement has also been investigated. It was found that the experimental results were strongly dependent on the material type, history of the specimen, stress level, and the time scale of the measurement.

The stress dependence of the piezoelectric d coefficient of piezoelectric and electrostrictive ceramic materials

An experiment has been developed to measure the piezoelectric d coefficient as a function of uniaxial stress on a piezoelectric or electrostrictive ceramic material. Measurements on piezoelectric ceramic specimens show that there is a very significant enhancement in the value of the piezoelectric coefficient as a function of applied stress with the value of the coefficient going up by a factor of about 2.5 over a 100-MPa range of applied stress. The increase in the piezoelectric coefficient continues until the stress is large enough for the ceramic to start depoling. Electrostrictive ceramics also show a similar trend, although their lack of mechanical strength prevents measurements over a large range of stress. Our results suggest that the performance of transducers can be enhanced by ensuring that the active piezoelectric material is under stress. [Funding support from the U.S. Office of Naval Research is gratefully acknowledged.]

Influence of stress state on high cycle fatigue of notched Ti-6Al-4V specimens

The high cycle fatigue (HCF) notch size effect is investigated for Ti-6Al-4V flat dogbone specimens with two notch sizes, each having an elastic stress concentration factor of K t=2.72. Points were generated on a constant life Haigh diagram using a step-loading technique. The notch size effect is compared with previous results obtained from circumferentially notched cylindrical specimens in terms of the biaxial state of stress at the notch root and von Mises effective stress. Within the range of dimensions tested, there is limited dependence of the fatigue limit upon the notch root radius. Stresses at the notch root and the fatigue notch factor are examined as a function of uniaxial stress, effective stress, notch plasticity, and notch root radius.

Linear and Nonlinear Elasticity of Granular Media: Stress-Induced Anisotropy of a Random Sphere Pack

We develop an effective medium theory of the nonlinear elasticity of a random sphere pack based upon the underlying Hertz-Mindlin theory of grain-grain contacts. We compare our predictions for the stress-dependent sound speeds against new experimental data taken on samples with stress-induced uniaxial anistropy. We show that the second-order elastic moduli, Cijkl, and therefore the sound speeds, can be calculated as unique path-independent functions of an arbitrary strain environment, {εkl}, thus generalizing earlier results due to Walton. However, the elements of the stress tensor, σij, are not unique functions of {εkl} and their values depend on the strain path. Consequently, the sound speeds, considered as functions of the applied stresses, are path dependent. Illustrative calculations for three cases of combined hydrostatic and uniaxial strain are presented. We show further, that, even when the additional applied uniaxial strain is small, these equations are not consistent with the usual equations of third-order hyperelasticity. Nor should they be, for the simple reason that there does not exist an underlying energy function which is simply a function of the current state of the strain. Our theory provides a good understanding of our new data on sound speeds as a function of uniaxial stress.

Uniaxial stress dependence of the [ζ ζ 0]-TA 2 anomalous phonon branch in Ni 2MnGa

Results of neutron scattering experiments on single crystals of Ni 2MnGa as a function of uniaxial stress and temperature are reported. Emphasis is placed on the behavior of the low-energy part of the [ζ ζ 0] TA 2 phonon branch and the associated premartensitic phase transformation. The dip in the phonon dispersion curve is stress-dependent and shifts from ζ = 0.33 for zero stress to ζ = 0.36 for an applied stress of 95 MPa. The energy of the soft phonon decreases with increasing stress. The premartensitic transition temperature is increased from 265 K in the unstrained sample to ≈ 300 K at 95 MPa.

Uniaxial-stress dependence of the phonon behavior in the premartensitic phase of Ni62.5Al37.5.

Results of neutron-scattering experiments on a single crystal of ${\mathrm{Ni}}_{62.5}$${\mathrm{Al}}_{37.5}$ as a function of uniaxial stress and temperature are reported. Emphasis is placed on the behavior of the low-energy part of the [\ensuremath{\zeta}\ensuremath{\zeta}0]-${\mathrm{TA}}_{2}$ phonon branch and its associated central peak. The dip in the phonon-dispersion curve is stress dependent and shifts from \ensuremath{\zeta}=0.14 for zero stress to \ensuremath{\zeta}=0.18 for an applied stress of 85 MPa at room temperature. As the temperature decreases the satellite shifts further, the phonon energy decreases considerably, and the linewidths become broad. These results are interpreted in terms of Clapp's localized soft-mode theory of nucleation in martensite.

DEPENDENCE OF ACOUSTOELASTIC CONSTANTS ON EXTERNAL MAGNETIC FIELDS

Abstract The dependence of acoustoelastic constants on external magnetic fields is experimentally investigated for JIS-SS41 mild steel specimens. In the case of ferromagnetic materials, the elastic wave velocities at a demagnetized state are slightly smaller than those at a highly magnetized state. This occurs due to the magnetoelastic interaction, which in turn depends on the stress state. In the present study, we measured the propagation velocities of longitudinal and shear waves in steel specimens as functions of uniaxial stress and external magnetic field. We found that in the demagnetized state, the velocity change with stress showed different slopes for compressive and tensile loading. The difference decreased as the specimens were magnetized, approaching its saturation. As for acoustoelastic birefringence, which measures the principal stress difference, the effect of magnetoelastic interactions is relatively weak, while for the longitudinal/shear wave velocity ratio, which is proportional to the sum of principal stresses, this effect may induce considerable errors. Magnetization of steel components is then recommended to improve the accuracy of acoustoelastic stress measurements. A discussion is given for the strength of magnetization required.