[Paper Review] Strong magnetoresistance in a graphene Corbino disk at low magnetic fields

Masahiro Kamada, Vanessa Gall+5 more|arXiv (Cornell University)|May 7, 2021

Graphene research and applicationsMaterials Science49 references23 citations

TL;DR

This study demonstrates an ultra-high magnetoresistance of 4000B²% in a suspended graphene Corbino disk at low magnetic fields (≤0.15 T), arising from intrinsic quantum transport effects. The effect, dominated by long-range Coulomb scattering and field-dependent screening of impurities, enables a magnetic field sensitivity of 60 nT/√Hz at 4 K, making it ideal for sensitive field sensing and intrinsic graphene characterization.

ABSTRACT

We have measured magnetoresistance of suspended graphene in the Corbino geometry at magnetic fields up to $B=0.15\,$T, i.e., in a regime uninfluenced by Shubnikov-de Haas oscillations. The low-temperature relative magnetotoresistance $[R(B)-R(0)]/R(0)$ amounts to $4000 B^2\% $ at the Dirac point ($B$ in Tesla), with a quite weak temperature dependence below $30\,$K. A decrease in the relative magnetoresistance by a factor of two is found when charge carrier density is increased to $|n| \simeq 3 imes 10^{-10}$ cm$^{-2}$. The gate dependence of the magnetoresistance allows us to characterize the role of scattering on long-range (Coulomb impurities, ripples) and short-range potential, as well as to separate the bulk resistance from the contact one. Furthermore, we find a shift in the position of the charge neutrality point with increasing magnetic field, which suggests that magnetic field changes the screening of Coulomb impurities around the Dirac point. The current noise of our device amounts to $10^{-23}$ A$^2$/$\sqrt{ extrm{Hz}}$ at $1\,$kHz at $4\,$K, which corresponds to a magnetic field sensitivity of $60$ nT/$\sqrt{ extrm{Hz}}$ in a background field of $0.15\,$T.

Motivation & Objective

• To investigate intrinsic magnetoresistance in suspended graphene Corbino disks at low magnetic fields, free from Shubnikov-de Haas oscillations.
• To characterize the role of long-range (Coulomb impurities, ripples) and short-range scattering in determining magnetoresistance.
• To determine the origin of the observed quadratic B² dependence of magnetoresistance and its weak temperature dependence.
• To explore the field-induced shift of the charge neutrality point and its implications for screening physics in graphene.
• To evaluate the device’s performance as a magnetic field sensor via current noise measurements.

Proposed method

• Fabricated suspended graphene Corbino disks using a lift-off resist (LOR) sacrificial layer technique, achieving high mobility (µmax ≈ 1–2×10⁵ cm²/Vs).
• Performed low-temperature (4 K and 27 K) magnetoresistance measurements in Corbino geometry with magnetic fields up to 0.15 T.
• Used cubic spline interpolation of R(Vg) data to extract the gate voltage dependence of the Dirac point and its magnetic field shift.
• Measured current noise spectra to determine magnetic field sensitivity, achieving 10⁻²³ A²/√Hz at 1 kHz and 4 K.
• Applied the Corbino disk resistance formula R(B) = (1/2π)ρxx(B) ln(rout/rin) to relate measured resistance to bulk resistivity.
• Correlated gate-dependent resistance with carrier density and used the Landau level fan diagram to extract gate capacitance Cg = 1.5×10⁻⁵ F/m².

Experimental results

Research questions

• RQ1 What is the origin of the strong quadratic magnetoresistance (B²) observed in suspended graphene Corbino disks at low fields?
• RQ2 How does the position of the charge neutrality point shift with increasing magnetic field, and what does this imply about screening of Coulomb impurities?
• RQ3 To what extent do long-range and short-range scattering mechanisms contribute to the observed magnetoresistance?
• RQ4 How does the magnetoresistance depend on carrier density, and what does this reveal about the role of impurities?
• RQ5 Can the intrinsic magnetoresistance in suspended graphene be leveraged for high-sensitivity magnetic field sensing?

Key findings

• The relative magnetoresistance reaches 4000B²% at the Dirac point with a weak temperature dependence below 30 K, indicating a robust intrinsic effect.
• A 50% reduction in relative magnetoresistance is observed when carrier density increases to |n| ≃ 3×10⁻¹⁰ cm⁻², indicating a suppression of the B² response at higher doping.
• The Dirac point shifts by ∆Vg = 5B V per Tesla, indicating that magnetic fields alter the screening of negatively charged Coulomb impurities near charge neutrality.
• The observed magnetoresistance is well described by a B² dependence with only small corrections up to 0.1 T, suggesting dominance of quantum corrections from long-range disorder.
• Current noise of 10⁻²³ A²/√Hz at 1 kHz corresponds to a magnetic field sensitivity of 60 nT/√Hz at 4 K in a 0.15 T background field.
• The device exhibits negligible V dependence (≤3% difference between V<0 and V>0 extrapolations), confirming high linearity and low noise in transport measurements.