Introduction to the NHMFL Pulsed Field Facility at LANL

Information on the physical set-up of pulsed field measurements

Read about lock-in amplifiers and their role in your measurements

Information about noise and ways to eliminate it from your measurements

How to collect and evaluate your measurement data

Information on optical spectroscopy

Information about time-resolved optics

Information on de Haas van Alphen Effect measurements

Information on Shubinkov de Haas Effect measurements

Information on Absolute Resistivity measurements

Information on Heat Capacity measurements

Information on RF Penetration Depth measurements

Absolute Resistivity


Associated Scientists: Chuck Mielke <cmielke@lanl.gov> or (505) 665-1500, Fedor Balakirev <fedor@lanl.gov> or (505) 665-5263

Most materials exhibit a change of resistance with applied magnetic fields (magnetoresistance) that is one of the most common transport measurements made at NHMFL. Magnetoresistance measurements contain information about a material's electronic structure, carrier mass, electron-phonon coupling, etc. 4 wires need to be attached to a sample to measure it's magnetoresistance. Ordinarily, resistance is measured by placing two probes of an ohm-meter across the ends of whatever is being measured.

2 wire measurements do not work very well for samples located in our experimental set-up because the samples are located at the bottom of a 1.5 meter long probe. The leads connecting the sample to the outside world have a resistance of ~25W. This makes it impossible to measure accurately the resistance of just the sample using the 2 lead measurement method if the sample resistance is less than 25W. The 4 wire resistance measurement method solves this problem.

For the 4 wire method, we pass a current through the sample (2 contacts), then measure the potential difference across the sample (2 more contacts). We then know that R = V/I between the voltage leads, which gives us just the resistance of the sample without the leads and contacts.