We report on low temperature susceptibility and magnetization measurements made on single crystals of the recently discovered heavy-fermion superconductor UTe$_2$ and compare the results with the two ambient pressure ferromagnetic superconductors URhGe and UCoGe. Hysteresis curves in the superconducting phase show a familiar diamond shape superimposed on a large paramagnetic background. The Meissner state was measured by zero field cooling in small fields of a few Oe as well as ac susceptibility measurements in small fields and resulted in 100\% shielding, with a sharp transition. However the field cooling Meissner-Ochsenfeld effect (expulsion of flux) was negligible in fields greater than just a few Oe, but becomes nearly 30\% of the perfect diamagnetic signal when the field was reduced to 0.01~Oe. The critical current due to flux pinning was studied by ac susceptibility techniques. Over the range in fields and temperature of this study, no signature of a ferromagnetic transition could be discerned. The lower critical field $H_{\rm c1}$ has been measured along the three crystalographic axes, and surprisingly, the anisotropy of $H_{\rm c1}$ contradicts that of the upper critical field. We discuss this discrepancy and show that it may provide additional support for a magnetic field-dependent pairing mediated by ferromagnetic fluctuations in UTe$_2$.
Theory of anomalous magnetotransport from mass anisotropy
在欠掺杂的YBa $_2$ Cu $_3$ O $_{6+x}$中，有证据表明在掺杂制度$ 0.12<p<0.16$中存在小的费米表面口袋，其受到实质性的质量增强。由于“热点”或其他相关的物理现象，这种质量增加在费米表面上可能会有很大的变化。因此，我们研究了具有大的有效质量各向异性的类电子费米口袋的磁输运。在弛豫时间近似，我们表明，即使是一个固定形状的口袋，霍尔效应的大小和符号可能会改变的质量各向异性的变化（除了在非常大的，可能无法访问的磁场）。我们讨论了最近的霍尔测量在近最佳掺杂的铜氧化物在高场的影响。此外，我们确定了一个新的中间渐近制度的磁场，其特征在于B-线性磁阻。类似的现象应该会发生在其他各种具有各向异性质量增强的实验系统中
Iridate oxides display exotic physical properties that arise from the interplay between a large spin-orbit coupling and electron correlations. Here, we present a comprehensive study of the effects of hydrostatic pressure on the electronic transport properties of SrIrO3 (SIO), a system that has recently attracted a lot of attention as potential correlated Dirac semimetal. Our investigations on untwinned thin films of SIO reveal that the electrical resistivity of this material is intrinsically anisotropic and controlled by the orthorhombic distortion of the perovskite unit cell. These effects pr…
Anomalous magnetic properties of multi-walled carbon nanotubes embedded with magnetic nanoparticles: Consistent with ultrahigh temperature superconductivity
我们报告的高温（300-1120 K）磁化数据的Fe和Fe 3 O 4纳米颗粒嵌入多壁碳纳米管。用高能同步辐射X射线衍射仪和电感耦合等离子体质谱仪精确测定了磁性杂质的含量。我们明确地表明，Fe和Fe 3 O 4纳米粒子的磁矩增强了约3倍，与他们预期的自由（未嵌入）磁性纳米粒子相比。磁化增强因子几乎与所施加的磁场无关，但显著地取决于冷却速率。更有趣的是，当样品被加热到1120 K时，增强的磁矩完全丧失，并且在1120 K时丧失的磁矩通过低于1020 K的几个热循环完全恢复。此外，在低于约60 K时，磁化强度迅速增加或减少。除了由于多壁碳纳米管中低温超导性的存在而产生的顺磁迈斯纳效应外，现有的物理模型无法解释这些反常的磁性。
The orbital effect on the anomalous magnetism and evolution of low La-doping single crystals, La$_x$Y$_{1-x}$VO$_{3}$ (x = 0, 0.1, and 0.2), has been investigated by applying the X-ray diffraction, specific heat, magnetization and Raman scattering techniques. The larger nearest-neighbor (NN) exchange interaction along c-axis stabilizes the fluctuant G-type orbital ordering (G-OO) which favors the exotic C-type antiferromagnetic order (C-AF). It is found that the NN exchange interaction in ab plane is anisotropy relating to the in plane magnetic anisotropy, which becomes smaller in high La-dope…
We report on the observation of temperature and field dependent anomalous Nernst effect (ANE) in Ni-rich bulk Ni-Co-Mn-Sn full Heusler alloy. A large change in the transverse Nernst coefficient (N) is obtained across the first order magnetostructural transition from a tetragonal martensite to a cubic austenite phase. The saturation of ANE and magnetic data appear to depend largely on the magnetic anisotropy of the device. Such change in the Nernst co-efficient may prove to be useful for switching applications controlled by temperature and magnetic field changes.
We show that a Weyl superconductor can absorb light via a novel surface-to-bulk mechanism, which we dub the topological anomalous skin effect. This occurs even in the absence of disorder for a single-band superconductor, and is facilitated by the topological splitting of the Hilbert space into bulk and chiral surface Majorana states. In the clean limit, the effect manifests as a characteristic absorption peak due to surface-bulk transitions. We also consider the effects of bulk disorder, using the Keldysh response theory. For weak disorder, the bulk response is reminiscent of the Mattis-Bardee…
A detailed study of charge transport in the paramagnetic phase of Ho0.8Lu0.2B12 strongly correlated antiferromagnet was carried out at temperatures 1.9-300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals with different orientation of normal vectors to the lateral surface of Ho0.8Lu0.2B12 samples were investigated in order to establish the changes in Hall effect due to the anisotropy, induced by (i) the electronic phase separation (dynamic charge stripes) and (ii) formation of the disordered cage-glass state below 60 K. It was demonstrated that in magnetic fields above 40 kO…
In the easy-plane regime of XXZ spin chains, spin transport is ballistic, with a Drude weight that has a discontinuous fractal dependence on the value of the anisotropy $Δ= \cos πλ$ at nonzero temperatures. We show that this structure necessarily implies the divergence of the low-frequency conductivity for generic irrational values of $λ$. Within the framework of generalized hydrodynamics, we show that in the high-temperature limit the low-frequency conductivity at a generic anisotropy scales as $σ(ω) \sim 1/\sqrtω$; anomalous response occurs because quasiparticles undergo Lévy flights. For ra…
We report on the anomalous magnetization dynamics of the cycloidally-modulated spin textures under the influence of uniaxial anisotropy in multiferroic $\mathrm{GaV_4S_8}$. The temperature and field dependence of the linear ac susceptibility [$χ_{1ω}^{\prime}(T,H)$], ac magnetic loss [$χ_{1ω}^{\prime\prime}(T,H)$], and nonlinear ac magnetic response [$M_{3ω}(T,H)$] are examined across the magnetic phase diagram in the frequency range $f = 10-10000$ Hz. According to recent theory, skyrmion vortices under axial crystal symmetry are confined along specific orientations, resulting in enhanced robu…
