Multiplexer on the 0.7 anomaly in quantum point contacts (SP Workshop)

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• Mr Pengcheng Ma (University of Cambridge, Semiconductor Physics Group)
• Wednesday 08 March 2017, 14:15-15:15
• Mott Seminar Room (Mott Building Room 531), Cavendish Laboratory.

If you have a question about this talk, please contact Teri Bartlett.

The ‘0.7 anomaly’ refers to an unexpected shoulder at ~0.7*(2e2/h) in the linear conductance of a quantum point contact (QPC) [1], which occurs as a result of electron-electron (e-e) interactions. However, its origin is still under debate over twenty years. We measured thousands of QPC devices using a multiplexer statistic technique [2-3] and try to experimentally verify a recent van Hove scenario theory [4] that governs the 0.7 anomaly, compared with the phenomenological model of spontaneous spin polarization. VG Dependence: By sweeping the split-gate voltage (VG), the 0.7 anomaly forms at the maximum of the van Hove ridge-like local density of states (LDOS), which amplifies the e-e interactions to be strongest and thus make the suppression of conductance largest. Ex Dependence: Decreasing the curvature of the longitudinal potential barrier (Ex) has qualitatively similar effects compared with increasing e-e interaction strength, in that both can cause the 0.7 anomaly more prominent. B Dependence: In low parallel field, the magnetoconductance depends quadratically on the field in the sub-open regime. This Fermi-liquid property links the magnetoresponse strength to the local spin susceptibility fluctuations, which is largest also at the maximum of LDOS .

Reference:

[1] K. J. Thomas et al Phys. Rev. Lett. 77, 135 (1996) [2] H. Al-Taie et al App. Phys. Lett. 102, 243102 (2013) [3] L. W. Smith et al Phys. Rev. Applied 5, 044015 (2016) [4] F. Bauer et al Nature 501, 73 (2013).

This talk is part of the Semiconductor Physics Group Seminars series.

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