22 February 2023 Wed 4 pm

A quantum point contact (QPC) is a fundamental quantum device with a narrow constriction between two electron reservoirs. The spontaneous formation of a localized spin in the constriction makes the QPC a quantum-dot-like device having Kondo couplings with both reservoirs. The localized spin at the center of the constriction moves away from the center as the side-gate voltage decreases, which signifies a symmetry breaking in the left-right  Kondo coupling. A quantum phase transition induced by this symmetry breaking was studied by analyzing the parameters that recovered the gate-voltage-dependent tunneling conductance line shapes reported in the experiment. The parameter indicating the difference between the left and right Kondo coupling strengths was chosen as the order parameter, and its critical exponent was obtained as \beta=0.373. Showing the non-analytic behavior of the first derivative of the zero-bias anomaly energy at the transition point was provided as additional evidence of the continuous phase transition.

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