We combine synchrotronbased infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and firstprinciples calculations to explore the properties of hafnia under compression. We find that pressure drives HfO
This content will become publicly available on December 26, 2024
The discovery of the fractional quantum Hall state (FQHS) in 1982 ushered a new era of research in manybody condensed matter physics. Among the numerous FQHSs, those observed at evendenominator Landau level filling factors are of particular interest as they may host quasiparticles obeying nonAbelian statistics and be of potential use in topological quantum computing. The evendenominator FQHSs, however, are scarce and have been observed predominantly in lowdisorder twodimensional (2D) systems when an excited electron Landau level is half filled. An example is the wellstudied FQHS at filling factor
 Award ID(s):
 2104771
 NSFPAR ID:
 10502053
 Publisher / Repository:
 PNAS
 Date Published:
 Journal Name:
 Proceedings of the National Academy of Sciences
 Volume:
 120
 Issue:
 52
 ISSN:
 00278424
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
More Like this

${}_{2}$ :7%Y from the mixed monoclinic ($P{2}_{1}/c$ )$+$ antipolar orthorhombic ($\mathit{Pbca}$ ) phase to pure antipolar orthorhombic ($\mathit{Pbca}$ ) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the$\mathit{Pbca}$ metastable state at 300 K. Compression also drives polar orthorhombic ($Pca{2}_{1}$ ) hafnia into the tetragonal ($P{4}_{2}/nmc$ ) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO${}_{2}$ . 
We report results of largescale groundstate density matrix renormalization group (DMRG) calculations on t
${t}^{\prime}$ J cylinders with circumferences 6 and 8. We determine a rough phase diagram that appears to approximate the twodimensional (2D) system. While for many properties, positive and negative${t}^{\prime}$ values (${t}^{\prime}/t=\pm 0.2$ ) appear to correspond to electron and holedoped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. The${t}^{\prime}<0$ (holedoped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermi surface of the holedoped cuprates. However, we find${t}^{\prime}<0$ strongly suppresses superconductivity. The${t}^{\prime}>0$ (electrondoped) region shows the expected circular Fermi pocket of holes around the$\left(\pi ,\pi \right)$ point and a broad lowdoped region of coexisting antiferromagnetism and dwave pairing with a triplet p component at wavevector$\left(\pi ,\pi \right)$ induced by the antiferromagnetism and dwave pairing. The pairing for the electron lowdoped system with${t}^{\prime}>0$ is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker dwave pairing and striped pwave pairing appears. In a small doping region near$x=0.08$ for${t}^{\prime}\sim 0.2$ , we find an unconventional type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped twoleg ladder regions in between mimic the shortranged spin correlations seen in twoleg Heisenberg ladders. 
Charge transport in solids at low temperature reveals a material’s mesoscopic properties and structure. Under a magnetic field, Shubnikov–de Haas (SdH) oscillations inform complex quantum transport phenomena that are not limited by the ground state characteristics and have facilitated extensive explorations of quantum and topological interest in two and threedimensional materials. Here, in elemental metal Cr with two incommensurately superposed lattices of ions and a spindensitywave ground state, we reveal that the phases of several lowfrequency SdH oscillations in
${\sigma}_{\mathit{xx}}\left({\rho}_{\mathit{xx}}\right)$ and${\sigma}_{\mathit{yy}}\left({\rho}_{\mathit{yy}}\right)$ are no longer identical but opposite. These relationships contrast with the SdH oscillations from normal cyclotron orbits that maintain identical phases between${\sigma}_{\mathit{xx}}\left({\rho}_{\mathit{xx}}\right)$ and${\sigma}_{\mathit{yy}}\left({\rho}_{\mathit{yy}}\right)$ . We trace the origin of the lowfrequency SdH oscillations to quantum interference effects arising from the incommensurate orbits of Cr’s superposed reciprocal lattices and explain the observed$\pi $ phase shift by the reconnection of anisotropic joint open and closed orbits. 
In the physics of condensed matter, quantum critical phenomena and unconventional superconductivity are two major themes. In electrondoped cuprates, the low critical field (H_{C2}) allows one to study the putative quantum critical point (QCP) at low temperature and to understand its connection to the longstanding problem of the origin of the high
T_{C} superconductivity. Here we present measurements of the lowtemperature normalstate thermopower (S ) of the electrondoped cuprate superconductor La_{2−x}Ce_{x}CuO_{4}(LCCO) fromx = 0.11–0.19. We observe quantum critical$\mathit{S}/\mathit{T}$ versus$\mathbf{l}\mathbf{n}\left(\mathbf{1}/\mathit{T}\right)$ behavior over an unexpectedly wide doping rangex = 0.15–0.17 above the QCP (x = 0.14), with a slope that scales monotonically with the superconducting transition temperature (T_{C} with H = 0). The presence of quantum criticality over a wide doping range provides a window on the criticality. The thermopower behavior also suggests that the critical fluctuations are linked withT_{C} . Above the superconductivity dome, atx = 0.19, a conventional Fermiliquid$\mathit{S}\propto \mathit{T}$ behavior is found for$\mathit{T}\le $ 40 K. 
We present measurements of thermally generated transverse spin currents in the topological insulator Bi_{2}Se_{3}, thereby completing measurements of interconversions among the full triad of thermal gradients, charge currents, and spin currents. We accomplish this by comparing the spin Nernst magnetothermopower to the spin Hall magnetoresistance for bilayers of Bi_{2}Se_{3}/CoFeB. We find that Bi_{2}Se_{3}does generate substantial thermally driven spin currents. A lower bound for the ratio of spin current density to thermal gradient is
$\frac{{J}_{s}}{{\mathbf{\nabla}}_{\mathit{x}}\mathit{T}}$ = (4.9 ± 0.9) × 10^{6}$\left(\frac{\hslash}{2e}\right)\frac{\mathbf{A}\mathbf{\text{}}{\mathbf{m}}^{\mathbf{}\mathbf{2}}}{\mathbf{K}\mathbf{\text{}}\text{\mu}{\mathbf{m}}^{\mathbf{}\mathbf{1}}}$ , and a lower bound for the magnitude of the spin Nernst ratio is −0.61 ± 0.11. The spin Nernst ratio for Bi_{2}Se_{3}is the largest among all materials measured to date, two to three times larger compared to previous measurements for the heavy metals Pt and W. Strong thermally generated spin currents in Bi_{2}Se_{3}can be understood via Mott relations to be due to an overall large spin Hall conductivity and its dependence on electron energy.