We report results of largescale groundstate density matrix renormalization group (DMRG) calculations on t
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
 Award ID(s):
 1708334
 NSFPAR ID:
 10087945
 Publisher / Repository:
 Proceedings of the National Academy of Sciences
 Date Published:
 Journal Name:
 Proceedings of the National Academy of Sciences
 Volume:
 116
 Issue:
 13
 ISSN:
 00278424
 Page Range / eLocation ID:
 p. 59915994
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
More Like this

${t}^{\prime}$ 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. 
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. 
Abstract Single crystals of the quasiskutterudite compounds Ca_{3}(Ir_{1x}Rh_{x})_{4}Sn_{13}(3–4–13) were synthesized by flux growth and characterized by xray diffraction, energy dispersive xray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature,
, varies from 7 K in pure Ir ( ${T}_{\mathrm{c}}$x = 0) to 8.3 K in pure Rh (x = 1). Temperaturedependent electrical resistivity reveals monotonic suppression of the CDW transition temperature,T _{CDW}(x). The CDW starts in pure Ir,x = 0, atT _{CDW}≈ 40 K and extrapolates roughly linearly to zero at 0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The lowtemperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above ${x}_{c}\approx $ shows signs of nonFermi liquid behavior in a conelike composition pattern. We conclude that the Ca_{3}(Ir_{1x}Rh_{x})_{4}Sn_{13}alloy is a good candidate for a compositiondriven quantum critical point at ambient pressure. ${T}_{\mathrm{c}}$ 
Abstract We measure the thermal electron energization in 1D and 2D particleincell simulations of quasiperpendicular, lowbeta (
β _{p}= 0.25) collisionless ion–electron shocks with mass ratiom _{i}/m _{e}= 200, fast Mach number –4, and upstream magnetic field angle ${\mathcal{M}}_{\mathrm{ms}}=1$θ _{Bn}= 55°–85° from the shock normal . It is known that shock electron heating is described by an ambipolar, $\stackrel{\u02c6}{\mathit{n}}$ parallel electric potential jump, ΔB ϕ _{∥}, that scales roughly linearly with the electron temperature jump. Our simulations have –0.2 in units of the preshock ions’ bulk kinetic energy, in agreement with prior measurements and simulations. Different ways to measure $\mathrm{\Delta}{\varphi}_{\parallel}/(0.5{m}_{\mathrm{i}}{{u}_{\mathrm{sh}}}^{2})\sim 0.1$ϕ _{∥}, including the use of de Hoffmann–Teller frame fields, agree to tensofpercent accuracy. Neglecting offdiagonal electron pressure tensor terms can lead to a systematic underestimate ofϕ _{∥}in our lowβ _{p}shocks. We further focus on twoθ _{Bn}= 65° shocks: a ( ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}4$ ) case with a long, 30 ${\mathcal{M}}_{\mathrm{A}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}1.8$d _{i}precursor of whistler waves along , and a $\stackrel{\u02c6}{\mathit{n}}$ ( ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}7$ ) case with a shorter, 5 ${\mathcal{M}}_{\mathrm{A}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}3.2$d _{i}precursor of whistlers oblique to both and $\stackrel{\u02c6}{\mathit{n}}$ ;B d _{i}is the ion skin depth. Within the precursors,ϕ _{∥}has a secular rise toward the shock along multiple whistler wavelengths and also has localized spikes within magnetic troughs. In a 1D simulation of the , ${\mathcal{M}}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}=\phantom{\rule{0.25em}{0ex}}4$θ _{Bn}= 65° case,ϕ _{∥}shows a weak dependence on the electron plasmatocyclotron frequency ratioω _{pe}/Ω_{ce}, andϕ _{∥}decreases by a factor of 2 asm _{i}/m _{e}is raised to the true proton–electron value of 1836. 
Abstract One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, the
z axis) with frequencyω _{0}due to absorption of lowpower microwaves of frequencyω _{0}under the resonance conditions and in the absence of any applied bias voltage. The twodecadesold ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component of spin current vector ${I}^{{S}_{z}}$ is timeindependent while $({I}^{{S}_{x}}(t),{I}^{{S}_{y}}(t),{I}^{{S}_{z}})\propto {\omega}_{0}$ and ${I}^{{S}_{x}}(t)$ oscillate harmonically in time with a single frequency ${I}^{{S}_{y}}(t)$ω _{0}whereas pumped charge current is zero in the same adiabatic $I\equiv 0$ limit. Here we employ more general approaches than the ‘standard model’, namely the timedependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin $\propto {\omega}_{0}$ and charge ${I}^{{S}_{\alpha}}(t)$I (t ) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiples of the driving frequency $N{\omega}_{0}$ω _{0}. The cutoff order of such high harmonics increases with SOC strength, reaching in the onedimensional FM or AFM models chosen for demonstration. A higher cutoff ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 11$ can be achieved in realistic twodimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures. ${N}_{\mathrm{m}\mathrm{a}\mathrm{x}}\simeq 25$