Normal state
Introduction
The normal state, in the context of condensed matter physics, refers to the state of a material at conditions where it does not exhibit any form of quantum phenomena or other exotic behavior. This state is typically found at higher temperatures and is often contrasted with the superconducting state, ferromagnetic state, or other quantum phases that may occur under certain conditions.
Description
The normal state is characterized by the absence of long-range quantum coherence, which is a hallmark of many quantum phases of matter. Instead, the behavior of the material can often be described by classical physics, with quantum effects playing a minor role. In this state, the electrical resistance of a material is finite and typically increases with temperature, in contrast to the superconducting state where the resistance drops to zero.
Properties
The properties of materials in the normal state can vary widely, depending on the specific material and its atomic or molecular structure. However, some general properties can be described.
Electrical Conductivity
In the normal state, materials exhibit a finite electrical conductivity, which can vary from very low (in the case of insulators) to very high (in the case of conductors). The conductivity is typically temperature-dependent, with the resistance increasing as the temperature increases.
Thermal Conductivity
The thermal conductivity of a material in the normal state is also finite and typically decreases with increasing temperature. This is in contrast to the superconducting state, where the thermal conductivity can become infinite.
Magnetic Properties
In the normal state, materials can exhibit a range of magnetic behaviors, from diamagnetism (where the material is repelled by a magnetic field) to paramagnetism (where the material is attracted to a magnetic field). However, they do not exhibit the long-range magnetic order found in ferromagnetic or antiferromagnetic materials.
Transition to Other States
Under certain conditions, a material in the normal state can transition to another state, such as the superconducting state or a magnetic state. These transitions are often driven by changes in temperature, pressure, or magnetic field.
Superconducting Transition
The transition from the normal state to the superconducting state occurs when the temperature is lowered below a certain critical temperature. This transition is accompanied by a sudden drop in electrical resistance to zero, and is a quantum phase transition.
Magnetic Transition
A transition to a magnetic state, such as the ferromagnetic or antiferromagnetic state, can occur when the temperature is lowered below a certain critical temperature. This transition is also a quantum phase transition and is accompanied by the appearance of long-range magnetic order.