High-Pressure Transport Studies in 2H-NbSe${}_2$

The transition metal dichalcogenide 2H-NbSe${}_2$ has well-documented charge density wave (CDW) and superconducting transitions at 33 K and 7 K at ambient pressure. The CDW transition is suppressed under high pressure and is absent beyond the quantum critical point (QCP) at 4.6 GPa. The effect of this QCP on superconductivity is of great interest and stimulates discussions on the relation between superconductivity and the CDW order. So far, resistivity and X-ray measurements have explored the vicinity of this QCP, and they indicate only a weak relation between superconductivity and the CDW: either a weak competition between CDW order and superconductivity or a weak promotion of superconductivity by fluctuations at the CDW QCP. Here, we present high-pressure Hall effect measurements as a clear probe of the CDW order. We use patterned moissanite anvil cells for pressures well beyond the QCP.