Related Experiment Video
Updated: May 4, 2026
15:58
Measurement of Coherence Decay in GaMnAs Using Femtosecond Four-wave Mixing
Published on: December 3, 2013
8.6K
Spontaneous coherence in a cold exciton gas
A A High1, J R Leonard, A T Hammack
1Department of Physics, University of California at San Diego, La Jolla, California 92093-0319, USA. alex.high@gmail.com
Nature
|March 23, 2012
Summary
Researchers observed spontaneous coherence in cold exciton gases, a key characteristic of Bose-Einstein condensation. This finding in indirect excitons provides insights into quantum physics in solids.
Area of Science:
- Quantum physics
- Condensed matter physics
- Solid-state physics
Background:
- Bosonic particles form coherent states below quantum degeneracy temperature.
- Spontaneous coherence underlies phenomena like superconductivity and Bose-Einstein condensation.
- Excitons, bound electron-hole pairs, serve as a model for cold bosons in solids.
Purpose of the Study:
- To investigate spontaneous coherence in a gas of indirect excitons.
- To explore quantum physics of cold bosons in solids using indirect excitons.
- To characterize the emergent coherent state in indirect exciton gases.
Main Methods:
- Cooling indirect exciton gases below the quantum degeneracy temperature.
- Measuring spontaneous coherence and coherence length.
- Observing polarization patterns and phase singularities.
Main Results:
- Spontaneous coherence observed in macroscopically ordered exciton states and polarization vortices.
- Coherence length significantly exceeds classical gas values, indicating condensate-like behavior.
- Extended spontaneous coherence correlates with spontaneous polarization, revealing multicomponent coherent states.
- Phase singularities observed in the coherent exciton gas.
Conclusions:
- Indirect excitons exhibit spontaneous coherence below a few Kelvin.
- The observed phenomena are characteristic of a Bose-Einstein condensate in momentum space.
- This work demonstrates the potential of indirect excitons for studying quantum many-body physics in solids.
Related Concept Videos
01:23Atomic Nuclei: Nuclear Relaxation Processes
1.1K
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.
1.1K
01:08NMR Spectroscopy: Spin–Spin Coupling
3.4K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
3.4K
01:04IR Absorption Frequency: Delocalization
1.7K
Electron delocalization refers to the distribution of electrons across multiple atoms within a molecule rather than being confined to a single atom or bond. This phenomenon is common in systems with conjugated bonds—structures where alternating single and double bonds allow π-electrons to move freely across the network. The movement of electrons stabilizes the molecule and can affect various chemical properties, including vibrational frequencies observed in IR spectroscopy.
In IR...
In IR...
1.7K
01:12Kinetic Theory of an Ideal Gas
3.5K
A mole is defined as the amount of any substance that contains as many molecules as there are atoms in exactly 12 grams of carbon-12. An Italian scientist Amedeo Avogadro (1776–1856) formed the hypothesis that equal volumes of gas at equal pressure and temperature contain equal numbers of molecules, independent of the type of gas. Later, the hypothesis was developed to form the SI unit for measuring the amount of any substance.
The number of molecules in one mole is called...
The number of molecules in one mole is called...
3.5K
01:27Atomic Spectroscopy: Effects of Temperature
1.2K
Atomization, converting samples into gas-phase atoms and ions, is essential for atomic spectroscopy. The flame temperature required for atomization affects the efficiency of the atomic spectroscopic methods by increasing the atomization efficiency and the relative population of the excited and ground states.
At thermal equilibrium, the relative populations of excited and ground state atoms can be estimated using the Maxwell–Boltzmann distribution. For example, an increase in temperature...
At thermal equilibrium, the relative populations of excited and ground state atoms can be estimated using the Maxwell–Boltzmann distribution. For example, an increase in temperature...
1.2K
01:12Fermi Level Dynamics
1.1K
The vacuum level denotes the energy threshold required for an electron to escape from a material surface. It is usually positioned above the conduction band of a semiconductor and acts as a benchmark for comparing electron energies within various materials.
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
The work...
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
The work...
1.1K