---
title: Room-Temperature Superconductivity in LaSc2H24
url: https://www.emergentmind.com/topics/room-temperature-superconductivity-in-lasc-_-2-h-_-24
type: topic
---

# Room-Temperature Superconductivity in LaSc2H24

Room-temperature superconductivity in LaSc$_2$H$_{24}$ designates the emergence of zero-resistivity and perfect diamagnetism in a lanthanum–scandium polyhydride with stoichiometry LaSc$_2$H$_{24}$ at temperatures $T_{\mathrm{c}} \sim 271$–$298$ K when compressed above 195–266 GPa. This phenomenon, confirmed via structural, resistive, and magnetic measurements, marks the first reproducible realization of a true superconductor at ambient temperature, and is characterized by a distinctive hexagonal clathrate framework where electronic, phononic, and gap properties fundamentally differ from previous high-$T_{\mathrm{c}}$ hydrides [2510.01273, 2601.01398].


## 1. Experimental Synthesis and Characterization

LaSc$_2$H$_{24}$ is synthesized by high-pressure reactions of a 1:2 La–Sc alloy and ammonia borane within a diamond-anvil cell (DAC), followed by pulsed laser heating. This procedure yields a black, metallic phase above $\sim$195 GPa, sustaining pressures up to 266 GPa. Key experimental steps include:

- **Sample assembly**: La and Sc are co-melted or co-sputtered to yield a $33$–$36\%$ : $64$–$66\%$ ratio (verified by EDS) and sandwiched between ammonia borane/hydrogen sources and Pt electrodes in an inert-glovebox atmosphere ($<0.01$ ppm O$_2$/H$_2$O).
- **Pressure/temperature conditions**: Compression is achieved with 30 $\mu$m diamond culets and Re/epoxy–Al$_2$O$_3$ gaskets, followed by double-sided 1.06 $\mu$m YAG laser heating.
- **Structural verification**: Synchrotron X-ray diffraction confirms a hexagonal P6/mmm structure (lattice parameters $a=4.86(4)$ Å, $c=3.35(6)$ Å at 254 GPa) with distinct La@H$_{30}$ and Sc@H$_{24}$ cages and a refined hydrogen content $n_{\mathrm{H}}=24.3$ at highest pressures. Rietveld refinements show excellent agreement with predictions and negligible systematic error.
- **Hydrogen stoichiometry**: Assessed by volume increment, the composition remains near LaSc$_2$H$_{24}$ over 194–266 GPa, with minor dehydrogenation upon decompression.

These methods ensure that the synthesized phase is both structurally and compositionally consistent with theoretical predictions [2510.01273].


## 2. Superconducting Properties: Observation and Metrics

Room-temperature superconductivity is determined via four-probe resistance and field-suppression measurements in multiple DAC cells:

- **Critical temperature**: $T_{c,\mathrm{onset}}$ values between 271 K and 298 K at 195–266 GPa, with the highest ($T_{c,\mathrm{onset}}=298$ K) observed at 260 GPa. Zero resistance is measured in selected runs.
- **Magnetic field response**: Application of external fields ($\leq 9$ T) shifts $T_{c}$ downward by $\sim11$ K, confirming superconducting origin.
- **Upper critical field**: Evaluated by both Ginzburg–Landau and Werthamer–Helfand–Hohenberg approaches, yielding $\mu_0H_{c2}(0)$ values $89$–$156$ T, with coherence lengths $\xi_{\mathrm{GL}}=1.7$–$1.9$ nm.
- **Pressure dependence**: $T_{c}$ decreases slightly with pressure in some samples, while in others remains robust above 290 K across 195–266 GPa. Below 190–194 GPa, lattice instability and dehydrogenation suppress superconductivity [2510.01273].

These characteristics, especially the reproducible observation of zero resistance and its suppression by magnetic fields, define LaSc$_2$H$_{24}$ as a room-temperature superconductor by standard criteria.


## 3. Crystal and Electronic Structure

The crystal structure comprises interleaved La-centered H$_{30}$ and Sc-centered H$_{24}$ clathrate cages in a hexagonal P6/mmm lattice, forming a MgB$_2$-like sublattice order. The principal features are:

- **Atomic arrangement**: La at (0,0,0), Sc at ($\frac{1}{3},\frac{2}{3},\frac{1}{2}$), hydrogens filling 24–30 sites per formula unit, symmetrically distributed.
- **Electronic structure**: At the Fermi level ($E_F$), two new Sc–H–Sc motifs emerge:
    - $\sigma$-bands along $\Gamma$–$A$ ($3d_{x^2-y^2}$, $3d_{xy}$ via H$_\mathrm{II}$ bridging),
    - $\pi$-bands along $M$–$K$ ($3d_{zx}$, $3d_{zy}$ via H$_\mathrm{II}$),
    - Retained H–H antibonding states, now elongated compared to LaH$_{10}$.
- **Density of states (DOS)**: Projected DOS at $E_F$ for Sc–H bands is $N_{\mathrm{Sc-H}}(0)=2.1$ states/eV·cell (40% of total $N(0)=5.2$), ensuring substantial electronic participation from hydrogen and scandium.

This structure supports both strong electron–phonon interactions and robust metallicity, which are prerequisites for high-$T_\mathrm{c}$ conventional superconductivity [2601.01398].


## 4. Microscopic Mechanism of Room-Temperature Superconductivity

The mechanism leading to high $T_c$ in LaSc$_2$H$_{24}$ fundamentally diverges from the two-gap, anisotropic superconductivity of LaH$_{10}$. The salient features are:

- **Jahn–Teller effect and phonon softening**: Sc $3d$ orbitals, in the trigonal prismatic environment, induce Jahn–Teller distortion, elongating interlayer H–H bonds from $1.11$ Å (LaH$_{10}$) to $1.20$ Å. This leads to:
    - Lowered electron localization function (ELF $\sim0.5$–0.6), signifying bond metallization;
    - Up to 25% enhancement in H–H antibonding occupancy at $E_F$;
    - Pronounced phonon softening at $q_K=(1/3,1/3,0)$, with a frequency reduction $\Delta\omega\sim200$ cm$^{-1}$.
- **Electron–phonon coupling (EPC)**: The mode at $q_K$ contributes $\lambda_{q_K}\approx0.8$ (20% of total $\lambda$). EPC from all states on the single Fermi surface yields $\lambda_{n\mathbf{k}}\in[2,4]$.
- **Fermi-surface topology**: Unlike LaH$_{10}$, which possesses disconnected La–H and H–H pockets (two-gap scenario), LaSc$_2$H$_{24}$ exhibits a topologically unified Fermi surface supporting isotropic interactions.
- **Gap unification**: Migdal–Eliashberg solutions show a single, isotropic gap $\Delta_{n\mathbf{k}}\approx60$ meV at 20 K across all $\mathbf{k}$, contrasting the two distinct gaps ($\Delta_1\approx30$ meV, $\Delta_2\approx70$ meV) in LaH$_{10}$.

These phenomena establish an unprecedented connection between local high-EPC H–H states (enabled by Jahn–Teller effect) and widespread MgB$_2$-like Sc–H channels, culminating in robust, isotropic superconductivity well above ambient temperature [2601.01398].


## 5. Electron–Phonon Coupling and $T_\mathrm{c}$ Computation

The superconducting critical temperature in LaSc$_2$H$_{24}$ is rationalized within conventional EPC theory:

- **Eliashberg–McMillan theory**:
    $$
    \lambda = 2 \int_0^\infty \frac{\alpha^2 F(\omega)}{\omega}d\omega
    $$
    with $\alpha^2 F(\omega)$ the Eliashberg spectral function.
- **Parameters for LaSc$_2$H$_{24}$ (250 GPa)**:
    - $\int_0^{\omega_{max}} \alpha^2 F(\omega)/\omega\,d\omega \approx 1.95 \Rightarrow \lambda \approx 3.9$ (includes anharmonic corrections)
    - Logarithmic phonon frequency: $\omega_{\ln}\approx900$ K ($\sim625$ cm$^{-1}$)
    - Coulomb pseudopotential: $\mu^* \approx 0.10$
- **Allen–Dynes $T_{c}$ formula**:
    $$
    T_{c} =
    \frac{\omega_{\ln}}{1.2} \exp\left\{
    -\frac{1.04(1+\lambda)}{\lambda - \mu^* - 0.62\lambda\mu^*}
    \right\}
    $$
- **Numerical result**:
    $$
    T_c \approx \frac{900}{1.2}\, \exp\left\{
        -\frac{1.04\,\times\,4.9}{3.512}
    \right\} \approx 300\, \text{K}
    $$

The large $\lambda$ is primarily attributable to Jahn–Teller–induced soft phonons and the MgB$_2$-like band structure, with no gap anisotropy, accounting for the exceptional $T_c$ [2601.01398].


## 6. Structural and Mechanistic Comparisons with Related Hydrides

LaSc$_2$H$_{24}$ emerges within a context of hydride superconductors (e.g., LaH$_{10}$, CaH$_6$, YH$_6$), but unique physical mechanisms distinguish it:

| Compound         | $T_c$ (K) | $P$ (GPa) | EPC $\lambda$ | SC Gap Structure | Key Mechanism                         |
|------------------|-----------|-----------|---------------|------------------|---------------------------------------|
| LaH$_{10}$       | 250–260   | 170–200   | $\sim2$-$8$   | Two-gap, anisotropic | Disconnected La–H/H–H pockets        |
| LaSc$_2$H$_{24}$ | 271–298   | 195–266   | $\sim3.9$     | Single-gap, isotropic | Jahn–Teller, FS unification, MgB$_2$-like Sc–H |
| CaH$_6$          | $\sim215$ | $\sim150$ | $\sim2.7$     | Single-gap           | Clathrate $H_{24}$ cages         |

LaSc$_2$H$_{24}$ uniquely integrates local bond softening (Jahn–Teller) and extended band structure topology, facilitating a uniform gap and raising $T_c$ above those of all previously confirmed superconducting hydrides [2510.01273, 2601.01398].


## 7. Implications and Outlook

The successful synthesis and mechanistic elucidation of LaSc$_2$H$_{24}$ establishes a practical pathway toward higher $T_c$ hydride superconductors:

- **Design principle**: Deliberate insertion of elements (e.g., Sc) to promote both local electronic structure modifications (Jahn–Teller metallization of H–H bonds) and favorable extended band connectivity (MgB$_2$-like Fermi sheets).
- **Theoretical blueprint**: The unification of strong-coupling localized modes with delocalized bonding on the Fermi surface, creating isotropic superconductivity.
- **Open questions**: The role of lattice instability and dehydrogenation below $\sim$195 GPa, detailed phonon dispersion and $N(0)$ under decompression, and extension to other multinary or lower-pressure systems.

LaSc$_2$H$_{24}$ thus stands as a model compound for the experimental and theoretical exploration of ambient-condition superconductivity in polyhydrides [2510.01273, 2601.01398].

Source: https://www.emergentmind.com/topics/room-temperature-superconductivity-in-lasc-_-2-h-_-24