We describe how a local non-equilibrium nuclear polarisation can be generated and detected by electrical means in a semiconductor quantum point contact device. We show that measurements of the nuclear spin relaxation rate will provide clear signatures of the interaction mechanism underlying the "0.7" conductance anomaly. Our analysis illustrates how nuclear magnetic resonance methods, which are used extensively to study strongly-correlated electron phases in bulk materials, can be made to play a similarly important role in nanoscale devices.
Sum-over-states vs quasiparticle pictures of coherent correlation spectroscopy of excitons in semiconductors; femtosecond analogues of multidimensional NMR
Estimation of the electrical and thermal contact resistances and thermoemf of thermoelectric material-metal transient contact layer due to semiconductor surface rougness
A multiscale simulation approach is developed to simulate the contact transport properties between semimetal to a monolayer two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductor. The results elucidate the mechanisms for low contact resistance between semimetal and TMDC semiconductor contacts from a quantum transport perspective. The simulation results compare favorably with recent experiments. Furthermore, the results show that the contact resistance of a Bismuth-MoS2 contact can be further reduced by engineering the dielectric environment and doping the TMDC material to <1…
Interface-sensitive nuclear magnetic resonance at a semiconductor heterojunction using hyperpolarization
我们展示了一个界面敏感的NMR在半导体纳米结构，其中的一个模型异质结结构（在$_{0.48}$ Ga $_{0.52}$ P/GaAs）的微小异质结区域的NMR信号被检测到通过使用由光泵浦产生的核超极化。检测的关键是使用由于晶格失配而在异质结处发生的微小晶格畸变，这使我们能够在异质结处产生和定位超极化，并将其与其他部分区分开来。特别是，抑制核自旋扩散的空间变化的应变和由此产生的意外稳定的超极化在异质结是成功检测的关键。
Interface effects on an ultrathin Co film in multilayers based on the organic semiconductor Alq3
利用原子力显微镜、SQUID磁谱仪和核磁共振（NMR）研究了AlOx阻挡层厚度对Ta/Co/（AlOx）/Alq 3/Si混合结构磁性能和形貌的影响。所有使用的技术都指出，需要2nm的阻挡层厚度来在Alq 3的顶部上获得磁性良好的钴层。59 Co NMR测量结果表明，AlOx阻挡层导致形成具有“缺陷”钴的界面层，有利于具有良好磁性能的“大块”钴的生长。
Electrical contact resistance to two-dimensional (2D) semiconductors such as monolayer MoS_{2} is a key bottleneck in scaling the 2D field effect transistors (FETs). The 2D semiconductor in contact with three-dimensional metal creates unique current crowding that leads to increased contact resistance. We developed a model to separate the contribution of the current crowding from the intrinsic contact resistivity. We show that current crowding can be alleviated by doping and contact patterning. Using Landauer-Büttiker formalism, we show that van der Waals (vdW) gap at the interface will ultimat…
We demonstrate superconducting vertical interconnect access (VIA) contacts to a monolayer of molybdenum disulfide (MoS$_2$), a layered semiconductor with highly relevant electronic and optical properties. As a contact material we use MoRe, a superconductor with a high critical magnetic field and high critical temperature. The electron transport is mostly dominated by a single superconductor/normal conductor junction with a clear superconductor gap. In addition, we find MoS$_2$ regions that are strongly coupled to the superconductor, resulting in resonant Andreev tunneling and junction dependen…
Resistively-detected NMR (RDNMR) is a unique characterization method enabling highly-sensitive NMR detection for a single quantum nanostructure, such as a quantum point contact (QPC). In many studies, we use dynamic nuclear polarization and RDNMR detection in a quantum Hall breakdown regime of a local QPC filling factor of 1 ($ν_{\rm{qpc}} = 1$). However, the lineshapes of RDNMR signal are proved to be complicated and still not fully understood yet. Here, we systematically polarize the nuclear spins by current-pumping from the close vicinity of $ν_{\rm{qpc}} = 1$ conductance plateau all the wa…
Schottky barriers, emission regimes and contact resistances in 2H-1T' MoS$_2$ lateral metal-semiconductor junctions from first-principles
采用非平衡格林函数方法研究了场效应晶体管中二维沟道接触的2 H-1 T ' MoS $_2$横向金属-半导体（M-S）结的有限偏压输运性质.结果表明：（a）尽管线偶极子和平面偶极子的静电特性不同，但在二维和三维M-S结中，肖特基势垒高度对掺杂和外加偏压的响应是相似的;（b）2 H-1 T ' MoS $_2$横向结不受费米能级钉扎的影响;（c）扶手椅型界面具有比平面型更好的接触特性。Z字形界面，（d）与$p$沟道的1 T '接触将呈现相对于$n$沟道降低4-10倍的接触电阻，以及（e）与中间掺杂的$n$（$p$）沟道的接触在场（电子）发射状态下操作。我们还提供了一个改进的程序，以实验确定在2D材料结的发射制度。
Two-dimensional (2D) semiconductors are promising material candidates for next-generation nanoelectronics. However, there are fundamental challenges related to their metal-semiconductor (MS) contacts which limit the performance potential for practical device applications. In this work, we exploit 2D monolayer hexagonal boron nitride (h-BN) as an ultrathin decorating layer to form a metal-insulator-semiconductor (MIS) contact, and demonstrate a novel diode-like selective enhancement of the carrier transport through it. Compared to the conventional MS contact, the MIS contact dominated by both t…
Spin-helical states, which arise in quasi-one-dimensional (1D) channels with spin-orbital (SO) coupling, underpin efforts to realize topologically-protected quantum bits based on Majorana modes in semiconductor nanowires. Detecting helical states is challenging due to non-idealities present in real devices. Here we show by means of tight-binding calculations that by using ferromagnetic contacts it is possible to detect helical modes with high sensitivity even in the presence of realistic device effects, such as quantum interference. This is possible because of the spin-selective transmission p…
Ab initio simulation of the structure and transport properties of zirconium and ferromagnetic cobalt contacts on the two-dimensional semiconductor WS_2
Metal contacts to two-dimensional (2D) semiconductors are ubiquitous in modern electronic and optoelectronic devices. Such contacts are, however, often plagued by strong Fermi level pinning (FLP) effect which reduces the tunability of the Schottky barrier height (SBH) and degrades the performance of 2D-semiconductor-based devices. In this work, we show that monolayer MoSi$_2$N$_4$ and WSi$_2$N$_4$ - a recently synthesized 2D material class with exceptional mechanical and electronic properties - exhibit strongly suppressed FLP and wide-range tunable SBH when contacted by metals. An exceptionall…
The contact resistance between two dissimilar semiconductors is determined by the carrier transmission through their interface. Despite the ubiquitous presence of interfaces, quantitative simulation of charge transport across such interfaces is difficult, limiting the understanding of interfacial charge transport. This work employs Green's functions to study the charge transport across representative Si/Ge interfaces. For perfect interfaces, it is found that the transmittance is small and the contact resistance is high, not only because the mismatch of carrier pockets makes it hard to meet the…
