Spin-induced anomalous magnetoresistance at the (100) surface of hydrogen-terminated diamond

At a Glance

Metadata	Details
Publication Date	2016-10-13
Journal	Physical review. B./Physical review. B
Authors	T. Yamaguchi, Yosuke Sasama, Masashi Tanaka, Hiroyuki Takeya, Yoshihiko Takano
Institutions	University of Tsukuba, Waseda University
Citations	12
Analysis	Full AI Review Included

Technical Documentation & Analysis: Spin-Induced Anomalous Magnetoresistance in H-Terminated (100) Diamond

Executive Summary

This research demonstrates a critical step toward diamond-based spintronics by observing anomalous positive magnetoresistance (MR) in hydrogen-terminated (100) Single Crystal Diamond (SCD) surfaces. The key findings and implications are summarized below:

Anomalous Positive MR: A large, positive magnetoresistance was observed in H-terminated (100) SCD, contrasting sharply with the negative MR previously reported for (111) surfaces.
Spin-Dependent Transport: The MR magnitude is orders of magnitude larger than classical orbital MR, and its presence even when the magnetic field is parallel to the surface strongly suggests that the spin degree of freedom of the hole carriers is essential.
High Carrier Density: The ionic-liquid-gated field-effect-transistor (FET) technique successfully accumulated high hole carrier densities (up to 1.72 x 10¹³ cm^-2) necessary for low-temperature transport studies.
Universal Scaling: The in-plane magnetoresistance ratio ([ρ(B) - ρ(0)]/ρ(0)) collapses onto a single universal function of $B/T$ (Magnetic Field/Temperature), providing a strict constraint for developing new theoretical models of spin transport in diamond.
Material Requirement: The effect is attributed, in part, to the higher density of localized spins (dangling bonds) inherent to the reconstructed H-terminated (100) surface, emphasizing the need for high-quality, orientation-specific SCD substrates.
Spintronics Potential: The observed spin-dependent transport opens new avenues for developing robust, diamond-based spintronic devices leveraging diamond’s weak spin-orbit coupling and long coherence times.

Technical Specifications

The following hard data points were extracted from the transport measurements conducted on the hydrogen-terminated (100) SCD devices:

Parameter	Value	Unit	Context
Diamond Substrate Orientation	(100)	Crystal Plane	IIa-type Single Crystal Diamond (SCD) used.
Gate Voltage Range (V_g)	-1.4 to -1.8	V	Applied via ionic liquid gating to accumulate holes.
Hall Carrier Density (Maximum at 2 K)	1.72 x 10¹³	cm^-2	Achieved at V_g = -1.8 V.
Hall Mobility (Range at 2 K)	17 to 25	cm²/Vs	Measured mobility of the 2D hole gas.
Measurement Temperature Range	2.0 to 10.1	K	Range where anomalous positive MR was observed.
Applied Magnetic Field (B)	±7	T	Maximum field applied parallel (B //) and perpendicular (B ⊥) to the surface.
Surface Roughness (RMS)	0.2 to 0.5	nm	Measured over a 1 µm² area on the (100) surface.
In-Plane MR Scaling Function	[ρ(B) - ρ(0)]/ρ(0) ~ f(B/T)	N/A	Universal scaling observed across different V_g and temperatures.
Low-Field In-Plane Conductivity Scaling	[σ(B) - σ(0)]/σ(0) ≈ - 0.083(B/T)²	N/A	Parabolic dependence observed at small B/T ≤ 0.3 (T/K).

Key Methodologies

The experiment relied on precise material preparation and advanced low-temperature transport techniques:

Substrate Selection and Termination: IIa-type Single Crystal Diamond (SCD) wafers with (100) orientation were used and subjected to hydrogen termination to raise the energy bands and favor hole carrier introduction.
Device Patterning: A Hall bar geometry was defined on the diamond surface using photolithography and UV ozone treatment to serve as the channel for the FET.
Surface Cleaning: The sample was heated in an Argon (Ar) atmosphere to reduce the density of adsorbates prior to ionic liquid application.
Ionic Liquid Gating: N,N-diethyl-N-methyl-N-(2-methoxyethl)ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) ionic liquid was applied between the channel and a gate electrode.
Carrier Accumulation: A negative gate voltage (V_g) was applied at 220 K (above the ionic liquid’s glass transition temperature) to electrostatically accumulate the 2D hole gas.
Low-Temperature Transport: Resistance and Hall voltage measurements were performed in an ohmic region using a custom cryostat probe system at temperatures down to 2.0 K.

6CCVD Solutions & Capabilities

This research highlights the critical role of high-quality, orientation-specific Single Crystal Diamond (SCD) in advancing spintronics. 6CCVD is uniquely positioned to supply the necessary materials and customization services to replicate and extend this work.

Applicable Materials

To replicate or extend this research into diamond-based spintronics, researchers require the highest quality substrates:

Optical Grade Single Crystal Diamond (SCD): This material is essential. 6CCVD provides high-purity, low-defect SCD wafers in the required (100) orientation. The high purity (equivalent to IIa type) ensures minimal background defects, maximizing carrier mobility and spin coherence times.
Custom Hydrogen Termination: While the paper describes H-termination, 6CCVD can provide substrates ready for specific surface treatments or assist in developing optimized termination protocols for maximizing 2D hole gas quality.

Customization Potential

The fabrication of FETs and Hall bar structures demands precise material control and patterning capabilities, which 6CCVD offers:

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Ultra-Low Surface Roughness	Precision Polishing Service. Guaranteed Ra < 1 nm for SCD wafers.	Ensures the highest quality interface for the 2D hole gas, minimizing scattering and meeting or exceeding the 0.2-0.5 nm RMS roughness cited in the paper.
Custom Dimensions & Patterning	Custom Dimensions and Laser Cutting. We supply plates/wafers up to 125mm (PCD) and offer precise laser cutting and dicing services.	Allows researchers to define specific Hall bar or gate geometries (e.g., the 10 µm scale features shown in Fig. 1(a)) with high accuracy.
Ohmic Contact Metalization	In-House Metalization Services. Internal capability for depositing Au, Pt, Pd, Ti, W, and Cu.	Provides reliable, low-resistance ohmic contacts necessary for accurate low-current, low-temperature transport measurements, especially critical for spintronics applications.
Thickness Optimization	SCD Thickness Control. SCD layers available from 0.1 µm up to 500 µm.	Enables optimization of substrate thickness for integration into complex cryostat setups or for specific thermal management requirements.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD growth and material science for advanced electronic and quantum applications. We can assist researchers with material selection, orientation control, and surface preparation protocols for similar diamond-based spintronics or 2D hole gas transport projects. Our expertise ensures that the starting material meets the stringent requirements for observing subtle spin-dependent phenomena.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We report magnetoresistance measurements of hydrogen-terminated\n(100)-oriented diamond surfaces where hole carriers are accumulated using an\nionic-liquid-gated field-effect-transistor technique. Unexpectedly, the\nobserved magnetoresistance is positive within the range of 2<T<10 K and -7<B<7\nT, in striking contrast to the negative magnetoresistance previously detected\nfor similar devices with (111)-oriented diamond surfaces. Furthermore we find:\n1) magnetoresistance is orders of magnitude larger than that of the classical\norbital magnetoresistance; 2) magnetoresistance is nearly independent of the\ndirection of the applied magnetic field; 3) for the in-plane field, the\nmagnetoresistance ratio defined as [rho(B)-rho(0)]/rho(0) follows a universal\nfunction of B/T. These results indicate that the spin degree of freedom of hole\ncarriers plays an important role in the surface conductivity of\nhydrogen-terminated (100) diamond.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevb.94.161301