Quantum phase transition in few layer NbSe₂ probed through quantized conductance fluctuations

We present the first experimental observations of a quantum phase transition (QPT) between two distinct charge density wave (CDW) phases in 2-dimensional 2H-NbSe₂. Our studies were performed on suspended, ultra-thin 2H-NbSe₂ devices fabricated on piezoelectric substrates. We establish, through sensitive conductance fluctuation spectroscopy, that on varying the strain the system undergoes a QPT between the familiar triangular 3Q CDW phase and a novel linear 1Q CDW phase. With the help of mean-field calculations, these observations can be explained as to arise from dynamical phase transition between the two CDW states. To affirm this idea, we vary the lateral strain across the device via piezoelectric medium and map out the phase diagram near the quantum critical point (QCP). The results resolve a long-standing mystery of the anomalously large spectroscopic gap in the density of states of 2H-NbSe₂ measured through tunneling spectroscopy.