Low-temperature physicist

A low-temperature physicist investigates matter when thermal excitation is small enough for quantum behaviour to become especially prominent. Superconductivity, superfluidity and spin systems are characteristic subjects, although the temperature scale depends on the material and the effect being studied.

The central experimental problem is often controlling unwanted heat transfer while making a measurable electrical, magnetic or mechanical probe. A cryostat supplies a controlled low-temperature environment; thermometry and heat-leak measurements establish what the sample actually experiences. Reducing $k_{B}T$ relative to an excitation energy gap can suppress thermal populations, allowing a quantum ground-state response to be distinguished from a classical high-temperature one.

Charles Pence Slichter used nuclear magnetic resonance to test the microscopic physics of superconductivity. With L. C. Hebel, he measured nuclear spin-lattice relaxation in aluminium between 0.94 and 4.2 kelvin, using changes of magnetic field to separate relaxation in the superconducting state from detection in the normal state. The observed relaxation disagreed with a simple two-fluid account but could be understood through the electronic correlations of BCS theory. Nuclear spins thus acted as local probes of the superconducting electrons.^[ref]

Heinz London and Fritz London formulated the London equations in 1935 to describe the magnetic response of a superconductor. Zero electrical resistance alone does not specify expulsion of an existing magnetic field; their additional magnetic relation accounts for the Meissner effect. In a simple planar geometry it gives a field decaying into the material as $B(z)=B(0)e^{-z/{\lambda }_L}$, where ${\lambda }_L$ is the London penetration depth. Their phenomenological theory links a measurable penetration length to superconducting electrodynamics without supplying a microscopic pairing mechanism.^[ref]

Elephter Andronikashvili tested the two-fluid model of superfluidity by oscillating a stack of closely spaced disks in liquid helium-4. Viscous coupling makes the normal component follow the disks, adding to their effective moment of inertia; the superfluid component need not rotate with them. Measuring the oscillation period as temperature changes therefore estimates the normal-fluid fraction under the apparatus's entrainment conditions. The experiment turns an apparently unusual flow law into a mechanical measurement of two distinct contributions to one liquid.^[ref]

Fritz London and Heinz London formulated a phenomenological theory of the magnetic response of superconductors. Their equations make a static magnetic field decay over a finite London penetration depth, explaining field expulsion in the Meissner effect. This adds a physical condition beyond the acceleration of a perfectly conducting electron fluid. The London equations connect a measurable length scale with superconducting currents, providing a useful macroscopic description before a microscopic pairing theory was available.^[ref]

A physicist associated with the London dispersion force and London equations.

Frank Steglich coauthored an apparatus for measuring very small magnetostriction in pulsed magnetic fields. A fibre Bragg grating serves as an optical strain gauge attached to a small crystal: changes in its reflected wavelength report changes in length. The 2010 instrument resolved strain of order $10^{-7}$ with 47,000 hertz bandwidth and was demonstrated on gadolinium compounds at low temperatures. It connects an optical measurement to the way electronic and magnetic changes deform a solid.^[ref]

A physicist studying correlated electrons and emeritus director of the Max Planck Institute for Chemical Physics of Solids.^[ref]

John M. Martinis coauthored a 1985 observation of quantized energy levels in a current-biased Josephson junction. The relevant coordinate was the phase difference across an electrical circuit element, rather than the position of one isolated particle. The measured levels agreed with a quantum mechanics calculation using junction parameters measured in the classical regime. This showed that a fabricated superconducting circuit could possess a discrete excitation spectrum suitable for controlled quantum experiments.^[ref]

A physicist researching superconducting devices and quantum computers based on Josephson junctions.^[ref]

John Clarke coauthored experiments testing quantum mechanics through a macroscopic superconducting electrical circuit. In 1985, a current-biased Josephson junction exhibited quantized levels of its phase difference, with positions predicted from independently measured classical circuit parameters. The experiment connected precision electrical measurement with the discrete spectrum of a collective circuit coordinate.^[ref]

A physicist researching superconducting quantum interference devices and quantum-limited measurements.^[ref]

An experimental physicist whose advice on preparing superconducting films helped expose new behavior. According to Alexei Alexeyevich Abrikosov, Shalnikov urged keeping the deposition substrate at liquid-helium temperatures so metal atoms would remain in place rather than collect into droplets. The resulting films changed the measured critical-field behavior, showing how sample preparation can reveal physics hidden by an inhomogeneous specimen.^[ref]

Anthony Leggett developed a theoretical account of the newly discovered superfluid phases of helium-3. Unlike helium-4 atoms, helium-3 atoms are fermions, so their superfluid state involves correlated pairing. The internal spin and orbital structure of the pairs allows several distinct ordered phases. His account connected this structure with unusual nuclear magnetic resonance observations, using magnetic response to distinguish possible forms of the condensate. The work illustrates how a small interaction can make the internal symmetry of a quantum fluid experimentally visible.^[ref]

A physicist who studied superfluidity and macroscopic quantum mechanics at Illinois.^[ref]

Vitaly Ginzburg and Lev Landau described superconductivity through a spatially varying complex order parameter coupled to an electromagnetic vector potential. Their Ginzburg-Landau theory balances the cost of changing the order parameter with magnetic-field energy and the tendency to form a superconducting state. It predicts characteristic coherence and penetration lengths and supports analysis of surfaces, currents and nonuniform states. The theory is phenomenological: it can organize measurable behavior near a transition without first deriving the microscopic pairing interaction.^[ref]

A physicist who headed the Lebedev institute’s theoretical physics department from 1971 to 1988.^[ref]

Alexei Abrikosov showed how a type-II superconductor can admit magnetic flux while remaining superconducting over most of its volume. In the mixed state, circulating supercurrents surround vortex cores where the superconducting order parameter is suppressed. An array of these vortices can minimize the free energy between the lower and upper critical magnetic fields. The resulting vortex lattice explains a regime that lies between complete magnetic-field expulsion and destruction of superconductivity.^[ref]

A physicist who studied superconductivity at Argonne.^[ref]

An experimental condensed matter physicist who coauthored the discovery experiments on low-temperature phases of helium-3. Measurements in a Pomeranchuk cell revealed changes in the nuclear magnetic resonance signal at millikelvin temperatures, linking unusual pressure behavior to changes in the liquid's magnetic response. The observations supplied independent probes of the new quantum phases.^[ref]

Douglas Osheroff coauthored discovery experiments on the low-temperature phases of helium-3. Anomalies first seen during cooling prompted further measurements rather than immediately identifying the phase correctly. Subsequent nuclear magnetic resonance observations in a Pomeranchuk cell linked changes in the liquid's magnetic response to the new phases. Combining thermodynamic behavior with a separate magnetic probe helped establish that the surprising signal belonged to a new quantum state of the liquid.^[ref]

A physicist who conducted low-temperature research at Bell Laboratories and Stanford.^[ref]

David Morris Lee coauthored experiments establishing new low-temperature phases of liquid helium-3. Changes in nuclear magnetic resonance frequency and absorption below 3 millikelvin revealed a change in the liquid's magnetic response. These measurements supplied evidence beyond an anomaly in a cooling curve and helped discriminate among possible physical interpretations. The experiments opened a setting in which pairing, magnetic response and fluid motion can be studied together.^[ref]

A physicist whose Cornell research included helium at very low temperatures.^[ref]

K. Alex Müller and Georg Bednorz found evidence for superconductivity in copper-oxide compounds at unexpectedly high temperatures. Their 1986 barium-lanthanum-copper-oxygen samples contained multiple phases and showed a large electrical resistivity drop with onset in the 30 kelvin range. The strong dependence on applied current and sample connectivity required cautious interpretation. This initial result redirected the search for high-temperature superconductors toward chemically complex oxides.^[ref]

A solid-state physicist who carried out physics research at IBM.^[ref]

Georg Bednorz and K. Alex Müller investigated oxide compositions that displayed a striking electrical resistivity decrease on cooling. Their 1986 report described oxygen-deficient barium-lanthanum-copper compounds, with a superconducting-like onset in the 30 kelvin range. Because the samples contained several phases, a connected conducting path could dominate electrical resistance before the whole specimen behaved uniformly. The work connected materials chemistry and electrical measurements in the emergence of high-temperature superconductivity.^[ref]

A solid-state physicist who researched metallic oxides at IBM's Zurich laboratory.^[ref]

Ivar Giaever used electron tunnelling through a thin insulating barrier to measure the superconducting energy gap. The available electronic states on either side determine which tunnelling processes contribute at a given voltage. A gap suppresses low-energy current, so the current-voltage curve becomes a spectroscopic probe of the superconducting state. Following the feature with temperature connects an electrical measurement with a microscopic excitation energy, rather than merely demonstrating low resistance.^[ref]

A physicist.^[ref][ref]

John Robert Schrieffer coauthored the microscopic BCS theory of conventional superconductivity. Its many-electron ground state coherently combines configurations in which states of opposite spin and momentum are paired. An attractive interaction mediated by lattice vibrations can lower the energy of this collective state, while its excitations have a gap. The theory relates that construction to a phase transition, specific heat, magnetic-field penetration and other measurable properties of a superconductor.^[ref]

A physicist.^[ref]

Leon Cooper showed that a filled Fermi sea changes the physics of electron pairing. In the idealized problem, even a weak attractive interaction in an energy shell above the Fermi surface can produce a bound pair. The result concerns electrons in the presence of the filled sea, so it is not simply the problem of two isolated electrons in empty space. This instability supplied a key microscopic ingredient for BCS theory and the Cooper pair description of superconductivity.^[ref]

A physicist.^[ref][ref]

Pyotr Kapitsa measured extraordinarily small flow resistance in liquid helium below its lambda transition. Confining the flow to narrow passages made the failure of ordinary viscous-flow expectations experimentally striking. The observation helped establish superfluidity as a distinct quantum-fluid phenomenon. In a modern two-component interpretation, the low-resistance response does not mean that every component of the liquid has lost all viscous behavior; it motivates separating normal and superfluid contributions.^[ref]

A physicist.^[ref]

An experimental physicist who coauthored measurements of zero sound in liquid helium-3. At sufficiently low temperature, collisions become too infrequent to maintain ordinary local equilibrium during an acoustic cycle. The resulting collective response tests the theory of a Fermi liquid through propagation of a density disturbance.^[ref]

An experimental condensed matter physicist who coauthored an observation of zero sound in helium-3. The experiment probed a collective density wave in a regime where quasiparticle collisions are slow compared with the oscillation. This distinguishes collisionless quantum-fluid dynamics from ordinary hydrodynamic sound.^[ref]

An experimental physicist who coauthored the 1966 zero sound propagation experiment with Ansel Cochran Anderson and John Charles Wheatley. Sound measurements in very cold helium-3 tested whether collective density motion survives in the collisionless regime predicted for a Fermi liquid.^[ref]

John Bardeen and Walter Brattain connected semiconductor surface behavior with the operation of the point-contact transistor. Carrier injection near closely spaced contacts allowed a small input to control a larger electrical response, making amplification possible in a solid-state device.^[ref]

He later coauthored BCS theory, in which a coherent paired-electron ground state explains central properties of conventional superconductivity. This links microscopic interactions with an excitation gap and collective magnetic and thermal response.^[ref]

A physicist.^[ref]

An experimental condensed matter physicist who developed a low-temperature relaxation calorimeter for small samples. A sapphire platform is connected to a cold bath by a controlled thermal link; its temperature relaxation determines heat capacity. Explaining the platform's own thermal resistances is essential before interpreting a sample's small signal as a material property.^[ref]

Heike Kamerlingh Onnes liquefied helium, opening access to temperatures far below those reached with other common cryogenic liquids. This enabled electrical measurements through the low-temperature transition of metals and the discovery of superconductivity. His later liquid-helium experiments also investigated persistent currents, connecting the sharp resistance change with sustained electrical behavior in a closed circuit. The progression shows how a new cooling technique can expose phenomena that are inaccessible at higher temperatures.^[ref][ref]

A physicist.^[ref]

Helium liquefaction supplied a route to very low temperatures. The resistance-versus-temperature experiment for superconductivity and measurements of superconducting persistent current show how reaching those conditions opened new questions about electrical behavior.

Brian Josephson predicted that weakly coupled superconductors can carry a phase-dependent current. In the ideal Josephson effect, $I=I_c\sin \varphi$ relates the current to the condensates' phase difference, while $\dot{\varphi }=2eV/\hslash$ determines its evolution under a voltage. A constant voltage therefore gives an alternating current with frequency $2eV/h$. The relations make a macroscopic quantum phase measurable through electrical behavior and connect superconducting coherence with precision frequency and voltage experiments.^[ref]

Identity source: www.nobelprize.org/prizes/physics/1973/press-release/