This paper discusses transport methods for the investigation of the (Ga,Mn)As magnetic anisotropy. Typical magnetoresistance behaviour for different anisotropy types is discussed, focusing on an in depth discussion of the anisotropy fingerprint technique and extending it to layers with primarily uniaxial magnetic anisotropy. We find that in all (Ga,Mn)As films studied, three anisotropy components are always present. The primary biaxial along ([100] and [010]) along with both uniaxial components along the [110] and [010] crystal directions which are often reported separately. Various fingerprints of typical (Ga,Mn)As transport samples at 4 K are included to illustrate the variation of the relative strength of these anisotropy terms. We further investigate the temperature dependence of the magnetic anisotropy and the domain wall nucleation energy with the help of the fingerprint method.
Quantum Hall ferromagnets, cooperative transport anisotropy, and the random field Ising model
讨论了量子霍尔系统中自旋相反、填充因子接近1的两个朗道能级在面内磁场分量作用下能量重合时的行为。我们专注于在这些条件下对最近实验的解释[Zeitler等人，Phys. Rev. Lett. 86，866（2001）; Pan等人，Phys.Rev.B64，121305（2001）]，其中在低温下产生大的电阻各向异性。模拟伊辛量子霍尔铁磁体所涉及的系统，我们认为，这种运输各向异性反映域的形成所引起的随机场从各向同性样品表面粗糙度。
Spin relaxation was studied in a two-dimensional electron gas confined in a wide GaAs quantum well. Recently, the control of the spin relaxation anisotropy by diffusive motion was first shown in D. Iizasa et al., arXiv:2006.08253 (2020). Here, we demonstrate electrical control by drift transport in a system with two-subbands occupied. The combined effect of in-plane and gate voltages was investigated using time-resolved Kerr rotation. The measured relaxation time present strong anisotropy with respect to the transport direction. For an in-plane accelerating electric field along $\left[110\righ…
Helical edge modes of 2D topological insulators are supposed to be protected from time-reversal invariant elastic backscattering. Yet substantial deviations from the perfect conductance are typically observed experimentally down to very low temperatures. To resolve this conundrum we consider the effect of a single magnetic impurity with arbitrary spin on the helical edge transport. We consider the most general structure of the exchange interaction between the impurity and the edge electrons. Moreover, for the first time, we take into the account the local anisotropy for the impurity and show t…
Monolayer graphene and bilayer graphene have strikingly different properties. One such difference is the shape of the Fermi surface. Although anisotropic band structures can be detected in optical measurements, they have so far been difficult to detect in transport experiments on twodimensional materials. Here we describe a ballistic transport experiment using high-quality graphene that revealed Fermi surface anisotropy in the magnetoresistance. The shape of the Fermi surface is closely related with the cyclotron orbit in real space. Electron trajectories in samples with triangular lattices of…
We investigate the effect of the mass anisotropy on Friedel Oscillations, Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, screening properties, and Boltzmann transport in two dimensional (2D) metallic and doped semiconductor systems. We calculate the static polarizability and the dielectric function within the random phase approximation with the mass anisotropy fully taken into account without making any effective isotropic approximation in the theory. We find that carrier screening exhibits an isotropic behavior for small momenta despite the anisotropy of the system, and becomes strongly an…
In-Plane Anisotropy-Driven Directional Charge Transport in van der Waals p-n Heterojunction
Indian Association for the Cultivation of Science（印度科学文化促进协会）；Sincrotrone Trieste s.c.p.a.（的里雅斯特同步辐射中心）；Indian Institute of Technology Tirupati（蒂鲁帕提印度理工学院）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）
Anisotropic electronic transport is a possible route towards nanoscale circuitry design, particularly in two-dimensional materials. Proposals to introduce such a feature in patterned graphene have to date relied on large-scale structural inhomogeneities. Here we theoretically explore how a random, yet homogeneous, distribution of zigzag-edged triangular perforations can generate spatial anisotropies in both charge and spin transport. Anisotropic electronic transport is found to persist under considerable disordering of the perforation edges, suggesting its viability under realistic experimenta…
We develop a non-equilibrium Green's function formalism to study magnonic spin transport through a strongly anisotropic ferromagnetic insulator contacted by metallic leads. We model the ferromagnetic insulator as a finite-sized one-dimensional spin chain, with metallic contacts at the first and last sites that inject and detect spin in the form of magnons. In the presence of anisotropy, these ferromagnetic magnons become elliptically polarized, and spin conservation is broken. We show that this gives rise to a novel parasitic spin conductance, which becomes dominant at high anisotropy. Moreove…
The low in-plane symmetry in layered 1T'-ReS$_2$ results in strong band anisotropy, while its manifestation in the electronic properties is challenging to resolve due to the lack of effective approaches for controlling the local current path. In this work, we reveal the giant transport anisotropy in monolayer to four-layer ReS$_2$ by creating directional conducting paths via nanoscale ferroelectric control. By reversing the polarization of a ferroelectric polymer top layer, we induce conductivity switching ratio of >1.5x10$^8$ in the ReS$_2$ channel at 300 K. Characterizing the domain-defined …
We theoretically analyze the spectrum of a magnetic molecule when its charge and spin can couple to the molecular vibrations. More specifically, we show that the interplay between charge-vibron and spin-vibron coupling leads to a renormalization of the magnetic anisotropy parameters of the molecule. This effect is discussed for a model device consisting of an individual magnetic molecule embedded in a junction. We study the transport properties of the device and illustrate how the differential conductance is affected by the vibrationally induced renormalization of the magnetic anisotropy. Depe…
In this work, we theoretically study the magnon spin transport in easy-plane antiferromagnetic insulators in the presence of an in-plane magnetic field. By exactly calculating the magnon spectrum, we find the band splitting due to the magnetic anisotropy can be fully compensated by the external field at a particular strength, which makes its dynamics nearly equivalent to an easy-axis antiferromagnet. As a result, the intrinsic magnon spin Hall effect due to the dipole-dipole interaction, previously predicted in easy-axis antiferromagnets is activated in easy-plane antiferromagnets. The compens…
Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning
我们研究了一个流形的相互作用的弹性线的空间相关性的强烈影响随机和有序钉扎之间的竞争的一般问题。这是通过磁输运实验与YBa 2 Cu 3 O 7-d薄膜，包含一个周期性的涡旋钉扎阵列通过掩蔽离子照射，除了本地随机钉扎。我们观察到的强场匹配效应表明周期性钉扎的普遍存在，并表明在匹配场中每条涡旋线都束缚在人为钉扎位点上。然而，涡玻璃化转变的维度，准2D而不是通常的3D，证据减少沿涡线的涡玻璃相关性。这也支持了一个不寻常的角度依赖的磁阻，这大大不同于玻色玻璃系统。角磁阻的定量分析使我们能够将这种行为与系统各向异性的增强联系起来，这是离子辐照的附带效应。
A canonical quantization procedure is applied to the interaction of elastic waves --phonons-- with infinitely long dislocations that can oscillate about an equilibrium, straight line, configuration. The interaction is implemented through the well-known Peach-Koehler force. For small dislocation excursions away from the equilibrium position, the quantum theory can be solved to all orders in the coupling constant. We study in detail the quantum excitations of the dislocation line, and its interactions with phonons. The consequences for the drag on a dislocation caused by the phonon wind are poin…
High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus
二维晶体是纳米电子学的新兴材料。该领域的发展需要候选系统具有高载流子迁移率和与石墨烯相反的足够大的电子带隙。在这里，我们提出了一个详细的理论研究的原子和电子结构的少层黑磷（BP），以预测其电学和光学性质。该系统具有直接带隙，可调从1.51 eV的单层到0.59 eV的5层样品。我们预测的迁移率是空穴占主导地位，相当高，高度各向异性。该单层具有极高的空穴迁移率（约10000 cm $^{2}$ V $^{-1}$ s $^{-1}$）和反转各向异性的异常弹性性质。光吸收光谱表明垂直面内方向之间的线性二向色性，这允许光学测定的晶体取向和光学激活的各向异性传输特性。这些结果使少层BP成为未来电子学的一个有前途的候选者。
Nonreciprocal charge transport, which is frequently termed as electrical magnetochiral anisotropy (EMCA) in chiral conductors, touches the most important elements of modern condensed matter physics. Here, we have investigated the EMCA in Pt/PtMnGa (PMG) bilayers with the assitance of nonequilibrium fluctuation theorems. Large EMCA in the Pt/PMG bilayers can be attributed to nonreciprocal response of an interface-driven chiral transport channel. Due to the presence of large charge fluctuations for small current region, higher order EMCA coefficients should be added and they are all functions of…
Topological spin textures in an itinerant ferromagnet, SrRuO$_3$ is studied combining Hall transport measurements and numerical simulations. We observe characteristic signatures of the Topological Hall Effect associated with skyrmions. A relatively large thickness of our films and absence of heavy metal layers make the interfacial Dzyaloshinskii-Moriya interaction an unlikely source of these topological spin textures. Additionally, the transport anomalies exhibit an unprecedented robustness to magnetic field tilting and temperature. Our numerical simulations suggest that this unconventional be…
