# Synopsis: It takes two

The voltage created in inclined thin anisotropic films illuminated by laser light is significantly affected by a photovoltaic component.

A significant transverse voltage (more than $10\phantom{\rule{0.333em}{0ex}}\text{V}$) has been observed for several inclined-oriented anisotropic thin films when illuminated by laser light. This effect has been attributed to the off-diagonal thermoelectric effect, in which a temperature gradient orthogonal to the film plane induces a voltage parallel to the plane. However, recent results that deviate from the expected behavior of the thermoelectric effect have caused researchers to propose that the induced voltage may be due to an optical and hence nonthermal effect.

Writing in Physical Review B, Kouhei Takahashi and co-workers at Panasonic Corporation in Kyoto, Japan, present measurements of laser-induced voltages in ${\text{Ca}}_{x}{\text{Co0}}_{2}$ ($x\sim 0.5$) thin films at different laser wavelengths. The signals behave as expected for energies lower than the band gap of the film, but for energies above the band gap, the signal is smaller than what would be expected from the off-diagonal thermoelectric effect alone. This deviation is consistent with an interband transition, indicating that a small photovoltaic effect is suppressing the voltage signal. By revealing the nature of the different effects on the signal, this experiment helps resolve the controversy of the responsible effect. The results have bearing on applications such as sensitive thermal sensors and thermoelectric generators. – Brad Rubin

### Announcements

More Announcements »

## Previous Synopsis

Superconductivity

## Next Synopsis

Atomic and Molecular Physics

## Related Articles

Materials Science

### Viewpoint: Improving Electronic Structure Calculations

A new approach to calculating the properties of molecules and solids may offer higher accuracy at reasonable computational cost, accelerating the discovery of useful materials. Read More »

Optics

### Focus: Strong Light Reflection from Few Atoms

Up to 75% of light reflects from just 2000 atoms aligned along an optical fiber, an arrangement that could be useful in photonic circuits. Read More »

Optics

### Synopsis: Controlling a Laser’s Phase

A compact scheme can directly modulate the phase of a laser without a bulky external modulator. Read More »