Nonlocal Dierential Resistance in AlO xKTaO 3Heterostructures Patrick. W. Krantz Venkat Chandrasekhar Northwestern University

2025-05-02 0 0 4.9MB 8 页 10玖币

侵权投诉

Nonlocal Diﬀerential Resistance in AlOx/KTaO3Heterostructures

Patrick. W. Krantz,Venkat Chandrasekhar*

Northwestern University

2145 Sheridan Rd.

Evanston, Illinois, US, 60208

Email Address: v-chandrasekhar@northwestern.edu

Keywords: Complex Oxides, Cryogenic, Diﬀerential Resistance

Local and nonlocal diﬀerential resistance measurements on Hall bars deﬁned in AlOx/KTaO3heterostructures show anomalous be-

havior that depends on the crystal orientation and the applied back gate voltage. The local diﬀerential resistance is asymmetric in

the dc bias current, with an antisymmetric component that grows with decreasing gate voltage. More surprisingly, a large nonlocal

diﬀerential resistance is observed that extends between measurement probes that are separated by 100s of microns. The potential

source of this anomalous behavior is discussed.

Signiﬁcant attention has been paid to devices built on complex oxides for nearly two decades, and for

good reason. Since the advent of ﬁeld, sparked by the discovery of conductivity between resistive layers

of LaAlO3deposited on SrTiO3(STO) substrates [1], a number of properties have been shown to live

in the two dimensional electron gas (2DEG) at the interfaces of these complex oxide heterostructures.

These properties include superconductivity [2, 3, 4], strong spin-orbit interactions [5], and magnetism [6,

7], and have often been shown to coexist on the same sample [7, 8]. Importantly, these properties were

shown to be tunable with external parameters, such as an applied back gate voltage, Vg[5, 9, 10], gen-

erating a platform for further device development. Recently, focus has shifted to a new complex oxide,

KTaO3(KTO), which is similar to STO in some ways, but also has some signiﬁcant diﬀerences. For ex-

ample, like STO based heterostructures, KTO structures go superconducting but at signiﬁcantly higher

temperatures [11, 12, 13]. Another signiﬁcant diﬀerence is that KTO has a much larger spin orbit cou-

pling and a complex, crystal direction dependent spin texture[14]. One consequence of the large spin or-

bit interactions is the possibility of eﬃcient spin-charge conversion [15], making KTO a promising plat-

form for spintronic applications [16].

We report here anomalous low temperature local and nonlocal diﬀerential resistance measurements in

2DEGs that form at the interface between AlOxand KTO in the normal state. The local diﬀerential re-

sistance is asymmetric in the applied dc bias current, with the asymmetry increasing as the back gate

voltage Vgis decreased. A large nonlocal diﬀerential resistance is observed that also increases with de-

creasing Vg, and extends over lengths on the order of 100s of microns. The nonlocal diﬀerential resis-

tance depends on the speciﬁc probe conﬁguration used to measure it, and is greatly reduced or almost

completely disappears in certain conﬁgurations. This feature of the nonlocal signal rules out thermal ef-

fects, and suggests instead a chiral nature of charge transport as the source of the anomalous behavior.

The KTaO3substrates used in this study were 5 mm x 5 mm x 0.5 mm single side polished crystals

purchased from MSE Supplies LLC. Crystals with 3 diﬀerent surface orientations ((001), (110) and (111))

were processed identically, ﬁrst through a standard cleaning regimen of 3 min ultrasonication in acetone,

3 min ultrasonication in DI water and 3 min ultrasonication in isopropanol, then through photolithogra-

phy patterning using LOR-5A and S-1813 photoresists. The photolithography process deﬁned Hall bars

that were 50 µm wide with 600 µm between sets of voltage probes which had a 2 µm constriction deﬁn-

ing the contact point. The devices were realized using a series of 99.9995% aluminum depositions with

an electron-gun evaporator system. The deposited Al getters oxygen from the KTO surface, creating

oxygen vacancies that result in a conducting 2DEG, a procedure which was ﬁrst developed for generat-

ing 2DEGs on STO substrates [17]. The processing steps for these depositions were as follows: after an

arXiv:2210.12146v1 [cond-mat.mes-hall] 21 Oct 2022

in-situ oxygen plasma clean to remove any residual photoresist, a layer of 1.5 nm of aluminum was de-

posited onto the KTO substrates and allowed to sit for 10 min before several more 1.5 nm layers were

deposited to protect the device. The second and subsequent layers were completely oxidized by introduc-

ing 100 mTorr of oxygen into the chamber for 10 min before the application of the next layer. The result

was a resistive, amorphous AlOxover-layer and a 2DEG formed by the oxygen vacancies on the surface

[18]. Samples were then wirebonded to a header and aﬃxed at the bottom of a Oxford MX100 cryostat

equipped with a two axis superconducting magnet.

Diﬀerential resistance measurements were conducted by summing a low frequency sine wave from a

lock-in ampliﬁer (<20 Hz) with a dc voltage from an Agilent 33500B waveform generator. The output of

the summer was then used to drive a custom-built current source. Typical ac currents were 20 nA, and

for all measurements the dc and ac currents were applied along the same path. The voltage output from

the devices was ampliﬁed by a ﬁrst stage INA110 based pre-ampliﬁer before being read by the lock-ins

for the ac signal, and a HP34401A digital multimeter for the dc signal. The back gate voltage Vgwas

supplied by a Keithley KT2400 source equipped with a low pass ﬁlter and measured independently by

another HP34401A digital multimeter. Three diﬀerent measurement conﬁgurations based on Hall bar ge-

ometries were measured at ∼5K in these experiments, which are discussed in more detail below. It is

important to note that the resistance of these devices is quite high when compared to similar geometries

constructed from metals or cleaner 2DEGs [19, 20]. Thus, the scale of the sample resistance limits the

magnitude of the applied dc current Idc to 1 µA in this study.

Figure 1: (a) Schematic diagram of the Hall bar, showing measurement probes attached for a four terminal diﬀerential

resistance measurement. (b) Percent diﬀerential resistance (dV/dI) for the (001) sample showing a small, asymmetric de-

viation from constant resistance. (c) Percent (dV/dI) for the (110) sample showing signiﬁcantly more pronounced behavior

at lower gate voltages. (d) Percent (dV/dI) for the (111) showing the emergence of anti-symmetric peaks around a central

dip. All curves have been oﬀset by 0.5 % for clarity.

The ﬁrst measurement conﬁguration that we employed is the standard conﬁguration typically used

to measure the longitudinal resistance of a Hall bar. Current is applied along the length of the device,

and the resulting voltage measured between two probes on the same side, as shown in Fig. 1 (a). If the

current-voltage (IV) characteristic of the device is linear, the diﬀerential resistance dV/dI should be a

constant independent of the dc bias current Idc. While we expect a constant response, such a simple de-

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

NonlocalDierentialResistanceinAlOx/KTaO3HeterostructuresPatrick.W.Krantz,VenkatChandrasekhar*NorthwesternUniversity2145SheridanRd.Evanston,Illinois,US,60208EmailAddress:v-chandrasekhar@northwestern.eduKeywords:ComplexOxides,Cryogenic,DierentialResistanceLocalandnonlocaldierentialresistancemeasure...

展开>> 收起<<

Nonlocal Dierential Resistance in AlO xKTaO 3Heterostructures Patrick. W. Krantz Venkat Chandrasekhar Northwestern University.pdf

共8页,预览2页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Nonlocal Dierential Resistance in AlO xKTaO 3Heterostructures Patrick. W. Krantz Venkat Chandrasekhar Northwestern University

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: