Related Experiment Video
Updated: Aug 7, 2025
15:58
Measurement of Coherence Decay in GaMnAs Using Femtosecond Four-wave Mixing
Published on: December 3, 2013
5.8K
Diamagnetic response and phase stiffness for interacting isolated narrow bands.
1Department of Physics, Cornell University, Ithaca, NY 14853.
Summary
Researchers developed a new theory to calculate superconducting phase stiffness, crucial for high-temperature superconductivity. This framework sets an upper limit on transition temperatures in narrow-band materials without approximations.
Area of Science:
- Quantum Condensed Matter Physics
- Superconductivity Theory
Background:
- Superconductivity arises from electron pair coherence, with transition temperature (Tc) limited by microscopic mechanisms.
- Materials with quenched kinetic energy and dominant interactions are key for high-temperature superconductivity.
- Nonperturbative effects dominate when narrow electronic bands interact strongly.
Purpose of the Study:
- To develop a theoretical framework for computing electromagnetic response in generic Hamiltonians.
- To determine the maximum superconducting phase stiffness and its relation to Tc.
- To avoid mean-field approximations in analyzing superconductivity mechanisms.
Main Methods:
- Developed a theoretical framework to compute electromagnetic response for generic model Hamiltonians.
- Calculated superconducting phase stiffness by considering contributions from remote bands and density-density interactions.
- Applied the formalism to models of interacting flat bands, including topological and nontopological cases.
Main Results:
- Identified two key contributions to phase stiffness: integrating out remote bands and projected density-density interactions.
- Demonstrated that the framework provides an upper bound for phase stiffness and Tc.
- Validated the upper bound against numerically exact computations for a specific interacting flat band model.
Conclusions:
- The new theoretical framework accurately bounds superconducting phase stiffness and transition temperatures in narrow-band systems.
- Understanding these contributions is vital for designing novel high-temperature superconductors.
- The method offers a nonperturbative approach to a fundamental problem in condensed matter physics.
Related Concept Videos
01:14Diamagnetic Shielding of Nuclei: Local Diamagnetic Current
918
An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...
918
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.1K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.1K
01:26Diamagnetism
2.5K
Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets....
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets....
2.5K
01:27π Electron Effects on Chemical Shift: Overview
1.1K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.1K
01:23Atomic Nuclei: Nuclear Relaxation Processes
696
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis.
696
01:04¹³C NMR: ¹H–¹³C Decoupling
1.1K
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
1.1K