The 'phantom effect' in physics is finally observed in a laboratory

A new study reports the first experimental observation of the transverse Thomson effect – a long-hypothesized thermal effect that ties heat, electric current, and magnetic field into one neat result

The team showed that a thin bismuth antimony alloy changes temperature throughout its bulk when current, heat flow, and magnetic field point in three perpendicular directions.

They also showed that the sign of the temperature change flips when they reverse the magnetic field.

The transverse Thomson effect

Lead author Atsushi Takahagi of Nagoya University and collaborators at partner institutions report that this effect is distinct from the classical Thomson effect.

It unfolds when charge and heat move at right angles under a magnetic field, not when they run parallel.

In the classical Thomson effect, a conductor heats or cools inside its volume when a charge current flows along the same direction as a temperature gradient.

The Seebeck effect creates a voltage from a temperature difference, and the Peltier effect moves heat at a junction when current flows. An authoritative overview explains how these longitudinal effects differ from the transverse family.

Transverse effects couple perpendicular directions. The Nernst effect produces a sideways voltage from a heat flow in a magnetic field, and the Ettingshausen effect produces a sideways heat flow from an electric current in a magnetic field.

In the new observation, these two transverse effects act together to produce heating or cooling throughout the sample.

How the team finally saw it

The experiment used lock-in thermography, an imaging method that captures tiny temperature oscillations with high sensitivity.

The researchers drove an alternating current through the sample, recorded infrared images, and extracted only the thermal signal that oscillated with the current.

To isolate the transverse Thomson signal from other thermal effects, they repeated the measurement with and without an imposed temperature gradient.

They then subtracted the two data sets, removing edge signals tied to the Ettingshausen effect and revealing a clear volumetric temperature change across the bulk.

They chose Bi88Sb12, a bismuth antimony alloy known to exhibit a strong Nernst response near room temperature. That choice increased the odds that the transverse signal would be large enough to detect in a clean way.

The temperature maps showed a uniform modulation across the sample interior, not just at its boundaries. That uniform response is the hallmark of a bulk heat source or sink rather than an interface phenomenon.

The classic Thomson effect

The physics behind this new effect does not match what students usually learn about the standard Thomson effect. In the classic case, the strength of the effect depends only on how a material’s Seebeck coefficient shifts with temperature.

In the transverse version, the key factors instead come from the Nernst effect. Both the rate of change and the overall size of the Nernst response shape the outcome. This explains why flipping the magnetic field can turn heating into cooling.

One part of the effect drives the material to warm, while the other part makes it cool, and the balance tips depending on the direction and strength of the field.

Why this matters

Transverse thermoelectric devices can avoid the stacked junctions that limit traditional Seebeck or Peltier modules.

That geometry advantage, plus magnetic-field control, points to compact, localized thermal management that is easier to integrate in tight spaces.

There is also real momentum behind using Thomson physics to boost cooler performance. A recent report demonstrated a Thomson-effect-enhanced cooler that achieved a steady temperature span greater than 5 K at 38 K by exploiting an electronic phase transition.

Being able to switch a device from heating to cooling by flipping a field direction is practical. It can simplify feedback control for sensors, lasers, and chips that need stable temperatures.

The new result validates a measurement strategy that others can copy. It also supplies a target for modelers, since simulations must now match a full set of bulk, field-tunable temperature maps.

What comes next for materials

The study’s alloy gave a clean signal but left performance on the table because two internal contributions partly canceled each other.

Materials whose Nernst magnitude and its temperature derivative push in the same direction could yield much larger effects.

One promising route is to use semimetals that already show giant transverse responses. An influential paper reported an ultrahigh Nernst power factor in WTe2, highlighting how carrier mobility and band structure can amplify transverse signals.

Designers can also consider magnetic materials that deliver an anomalous Nernst effect without an external field.

That would eliminate magnets and shrink devices further, a theme emphasized in recent community summaries.

Improving measurement methods

In parallel, metrology will matter. Accurate extraction of tiny in-phase thermal signals remains tricky, so methods that combine imaging with careful boundary control should spread quickly.

The immediate use case is thermal management, but the scientific payoff is broader.

Transverse effects probe how electrons carry heat and respond to fields, so stronger signals open a window into transport physics in complex solids.

The work also bridges established thermoelectric thinking and newer transverse strategies. It invites device engineers to treat the Nernst coefficient as a design lever, not a curiosity.

The study is published in Nature Physics.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–